1 Introduction

According to the historical-cultural conception, the specifically human attributes of human beings, such as memory, volitional attention, language, thought, feeling, etc., i.e., consciousness, are understood as outcomes of life in an organized society based on labor activity. Qualitatively differing from other higher- level animals, work thus sets the beginning of the development of new needs that surpass the elementary ones, reaching the more complex levels of human conduct and existence (^{LEONTIEV, 1978}).

By creating the world of culture through labor, humans have their "nature," i.e., what is characteristic to them, socially determined. Therefore, they are no longer subjected to biological laws but to socio-historical laws that determine their existence (^{LEONTIEV, 1978}).

Given that the conditions of concrete life change over time, the processes of transmission and appropriation of human acquisitions from one generation to another become indispensable for individuals to become truly human (^{LEONTIEV, 1978}). Thus, the dialectical unity between these processes enables the continuity of historical progress.

In this context, as humans master the laws of nature and transform them through work, they create their own existence simultaneously, making effective their inherent humanity as representatives of the human species. Mediated by the transmission and assimilation process, that is, the teaching-learning process, the acquisition of human objectification results in the active formation of new psychic abilities and functions (^{LEONTIEV, 1978}).

According to Leontiev, "assimilation in humans is a reproduction process, in the individual's properties, of the historically-formed properties and abilities of the human species" (idem, p. 270, emphasis in the original). Thus,

Each generation begins its life in a world of objects and phenomena created by preceding generations. It appropriates itself of the richness of this world by participating in work, production, and various forms of social activity, thus developing the specifically human abilities which have crystallized, become embodied in this world (^{LEONTIEV, 1978}, p. 265).

In this sense, the author emphasizes that it is “out of the question that an individual's personal experience, as rich as it may be, is sufficient to produce the formation of abstract logical or mathematical thought and corresponding conceptual systems" (idem, p. 266). Given this assumption, Leontiev states that "not one life but a thousand would be needed" (ibid). In a historical-dialectical perspective of human development, each individual learns to be a human being.

Therefore, in essence, the human being is not conceived solely based on what is given biologically. They develop and are shaped over the time, learning to become truly human. The construction of their own individuality and existence is a fundamental educational process. In this sense, education is inseparable from the own human being origin. They acquire the specifically-human capabilities through the mediation and guidance of adults, who play a crucial role in the rapid appropriation of the essential characteristics of humanity by the child. These characteristics, rooted in the culture and society in which the child is born, are internalized by them, giving them the distinctive qualities that define the human condition. Therefore, the formation of the human being is intrinsically linked to education, which plays a central role in the transmission and appropriation of human achievements throughout history (^{SAVIANI, 2013}).

Based on these assumptions, ^{Davidov (1988}) highlights that the questions related to the development of human psyche and its attributes, as well as the driving forces behind it, are central problems in general, evolutionary, and pedagogical psychology. Investigations into this process seek to identify the connections between the development of higher psychological functions and the predominant teaching processes in education, sometimes perceived as parallel and thus independent and autonomous, sometimes as undifferentiated processes.

However, in order to truly understand the structure and dynamics that compose the periods of the formative process of the human psyche, which guarantee human beings the condition of universal beings, it is necessary, based on the assumptions of historical-cultural theory, to study human conduct historically. According to Vygotsky (²⁰¹²), this means understanding it in motion, which is the fundamental requirement of the historical-materialist dialectical method.

An investigation that encompasses the development process of a particular phenomenon in all its phases and changes, revealing its nature, allows humans to know themselves on their own essence. Therefore, it is only in motion that the individual demonstrates their existence, constituted by their multiple determinations. In this sense, scientific research becomes an indispensable path to know the reality beyond its appearance (^{VYGOTSKI, 2012}).

In opposition to the empirical-descriptive tendencies with which issues related to the development of the human psyche have been treated, as well as the determining role of school education on it, Vygotsky (¹⁹⁹⁶, p. 252, our translation) states that the true task of general psychology is to investigate what hides behind the external signs that serve as the "reflection" of development, that is, to investigate "the process of child development itself with its internal laws."

This means that to truly understand the logic that permeates psychic development, "we must give up on all intention of classifying ages by symptoms and start, as other sciences have done in their time, a periodization based on the internal essence of the studied process" (ibidem).

Therefore, the inconsistency of idealistic and mechanistic-materialistic conceptions, according to Vygotsky (1996), lies in the dualistic and non-dialectical methodological character on which these theories are based. According to the author, it prevents them from understanding the development of the psyche as a unique process, based on the principles of totality, mediation, and contradiction - central categories of the historical-materialist dialectical method. By dividing it into isolated periods that develop autonomously, they are apprehended separately from the concrete conditions of which individuals are part of, denying them.

Given these considerations, this paper develops itself based on the assumptions of Historical-Cultural Theory, whose philosophical and methodological unity is anchored on the historical-materialist dialectical method. Therefore, the objective is to present the principles on which the periodization of individual psychological development is based, guided by discussions, especially those of Vygotsky (¹⁹⁹⁶, ²⁰¹²), ^{Vigotski (2001}), ^{Leontiev (1978}, ²⁰¹⁰), ^{Elkonin (1987}), and ^{Davidov (1988}) in unity with educational processes, that is, the central foundations of human psyche development process in its relationship with school education.

2 Foundations of the Psychical Development Periodization

As highlighted by ^{Davidov (1988}) in the study of the periodization of human psychical development, the identification and comprehension of general principles that underlie its organization enable the distinction of corresponding developmental periods, explaining their psychological particularities, which vary throughout history. The childhood history study, for instance, reveals a childhood which extends itself over time, allowing for the identification of specific psychological changes within each period.

This premise is endorsed by ^{Leontiev (2010}), asserting that with each new generation and individual, certain life conditions may be identified, consequently, as the responsible for generating the content of their activity. Therefore, the understanding of activity content cannot surpass the concrete conditions in which development occurs.

Thus, it can be affirmed that "specific historical conditions exert influence both on the concrete content of an individual stage of development and on the overall course of the psychic development process as a whole" (^{LEONTIEV, 2010}, p. 65). The investigation of nature of psychological changes throughout development implies an examination of their "social nature," or rather, the "internal connection with the social demands imposed on the formation of man as the main link in the productive forces" (^{DAVIDOV, 1988}, p. 67, our translation).

Based on these statements, ^{Vygotski's (1996}) initial critique of predominantly descriptive investigative schemes of human psychical development is stabilized basing itself on three essential points. The first concerns the subjective nature of analyses in the face of objective developmental evidence; the second one lies in reducing the complexity of development to a single criterion which would delimitate all ages, and the third one has as the central focus the investigation the phenomenon based on its external indications.

Contrary to these conceptions, ^{Vygotski (1996}) argues that the true foundation of periodization lies in the internal changes of development itself. In the turning points of its course, a solid basis for determining the main periods of individuals' personality formation can be found. As the author highlights, "this viewpoint can capture something essential for the dialectical understanding of the process" (^{VYGOTSKI, 1996}, p. 253, our translation).

Thus, in his studies, ^{Vygotski (1996}) emphasizes the essentiality of neoformations occurring in each period, understanding them as formations that qualitatively reconfigure the structure of individuals' personality and activity. These psychological and social changes arise for the first time in each age and determine the consciousness, the individual's relationship with the environment, internal and external life and the entire course of development.

In this process, ^{Vygotski (1996}) underscores the need to understand the internal dynamics of each of these periods and the dynamics in the transition from one age to another, which alternate between stable and critical moments and are understood as turning points formed by essential changes in the development. As ^{Elkonin (1987}) highlights, the critical moments of the development confirm the assumption that the development is a dialectical process in which the transition from one idea to another occurs through a gradual yet revolutionary evolution.

Based on this assumption, ^{Leontiev (2010}) pays special attention to the study of development and activity content, considering it a focal point for understanding the driving forces that make the essential characteristics of each period effective.

According to the author, the analysis of activity content elucidates the central role of external life conditions, individual potentialities, and, similarly, the guiding role of education in determining individuals' attitudes towards the surrounding reality, psyche, and consciousness (^{LEONTIEV, 2010}).

This internal configuration or reconfiguration of each period of individuals' psychic life is termed by ^{Vygotski (1996}) as the "age structure," which posits a general thesis of the existence of a multitude of partial processes that integrate into a unique whole, governed by its own laws, determining the structure and course of each period. Thus, by structure, the author understands the global formations do not result from the mere sum of isolated and independent parts, as the idealistic and mechanistic conceptions would assume, but rather from the unity between parts and the whole.

As emphasized by ^{Vygotski (1996}, p. 261, our translation), "in each age period, development does not modify isolated aspects of the child's personality as it unfolds, restructuring the entire personality as a whole," instead, in the psychic development of individuals, there is necessarily an inverse dependence, "the child's personality changes in its internal structure as a whole, and the laws governing this whole determine the dynamics of each of its parts."

Therefore, in each period, a new central formation (central lines of development) is found, conceived as a guide for the entire process, characterizing the reorganization of the full child’s personality on a new base. It is all over around of this new central formation the other formations (the development accessory lines) are joint together and related, attributing to each age one specific, unique and unrepeatable structure (^{VYGOTSKI, 1996}).

^{Leontiev (2010}) views these new formations as essential aspects constituting the structure and dynamics of specifically human activity. In his studies, the author asserts that some activities are principal, guiding, or leading, while others are subsidiary in a given developmental period.

According to Leontiev (idem), we can affirm that each stage of psychic development is characterized by an explicit and primary relationship between the child and the surrounding reality; it is a precise and dominant type of activity that presupposes managing the fundamental changes of each age. However, it is crucial to emphasize that these changes are only possible to occur "when the required conditions are met," that is, under favorable concrete conditions (^{LEONTIEV, 1978}, p. 267).

Thus, ^{Leontiev (2010}) understands principal activity as the one whose form gives rise to other types of activities, while also differs from them; in which specific psychological processes and functions are formed and reorganized; also, on which the main psychological changes in the individual's personality depend on, observed as characteristics in each developmental period. Hence, the changes within each age, as well as the connections between new formations and between one period and another, rely on the existence and essentiality of a structure and dynamics unique to each developmental stage, ruled by the guiding activity in each period.

Therefore, as the general dynamics of the age, we base our understanding on ^{Vygotski's (1996}) studies, considering it a direct consequence of the structure, or the whole. The structure of each age and its specific attributes are transformed into a new age as the individual develops themselves. "The relationship between the whole and the parts, rather essential for understanding the structure, is a dynamic relationship that determines the changes and development of both the whole and the parts" (ibid, p. 262, our translation). This way, we understand dynamics as the set of all laws governing the formation, changes, and connections between new formations of each period's structure.

In this regard, ^{Leontiev (2010}) reiterates that the effective essential changes within each period's limits do not occur independently, but as processes of the human psychic life linked in one or another period. In other words, the current developmental period was 'prepared' within the previous period's intimacy, and likewise, the current period is also responsible for creating conditions for the succeeding period to unfold.

At this point, ^{Vygotski (1996}), ^{Leontiev (2010}), and ^{Elkonin (1987}) highlight the primary condition for defining the dynamics of each age: understanding the relationship between individuals' personality and the social environment to which they belong. Among the major theoretical and practical difficulties in developmental periodization is the apprehension of the social environment as something external to individuals, that is, as a set of objectives and independent conditions without any connection to them.

According to the aforementioned authors, under the influence of concrete conditions, individuals' position within the system of human relations, as well as their assimilation and intervention in the external world, that is, their activity, substantially changes over development. The real situation of the child from which "the world of human relations unfolds before them" is a condition determined by the objective position they occupy within these relations (^{LEONTIEV, 2010}, p. 60).

According to ^{Leontiev (2010}, p. 82):

The relations established between the child and the surrounding world are, by nature, social relations because it is precisely the society that constitutes the real, primary condition of their life, determining both its content and motivation. Each of the child's activities, therefore, does not merely express their relationship with objective reality. Existing social relations are also objectively expressed in each of their activities.

^{Vygotski (1996}) employs the term "social situation of development" to describe the specific form of relationship between the individual and the social environment. The social situation of each period determines the forms and course of development, enabling individuals to acquire new personality traits. As they develop, children become members of society, become aware of relationships and interpret them (^{LEONTIEV, 2010}).

Based on this premise, the social reality, as the primary source of development, also transforms social specificities into individual characteristics, endowing each human being with the character of a representative of the human species (^{LEONTIEV, 1978}; ^{VYGOTSKI, 1996}).

As mentioned earlier, the emergence of consciousness as a subjective image of objective reality results from a specific form of social existence (^{LEONTIEV, 1978}). New internal mechanisms and psychological functions are formed, bringing along a new way of perceiving and relating to the world and oneself (^{VYGOTSKI, 1996}). As emphasized by ^{Leontiev (2010}, p. 74), "any conscious act is shaped within an established circle of relationships, within this or that activity, which also determines its psychological peculiarity."

Regarding this peculiarity, ^{Leontiev's (2010}) study of activity content highlights that the psychological characteristic of this process is what the activity as a whole is directed toward. This means that the object of activity always coincides with the goal that stimulates the individual to perform it, that is, their reason. Therefore, activity is structured through multiple actions and operations, the latter being the socially determined form in which the activity is carried out.

Actions, on the other hand, are processes whose motive does not directly coincide with their goal, that is, with what they are directed toward. A concrete example given by ^{Leontiev (2010}) is as it follows: in a situation where a student starts reading a book in order to be prepared for an exam, this reading may not necessarily constitute an activity because its psychological nature (the reason) can be different, as analyzed below.

If, during the reading, the student realizes it is not necessary for the exam and decides to abandon the book, it is clear that the motive for reading was not the content of the book but the need to pass the exam. However, if, upon being informed of this, the student continues reading the book, it can be affirmed that the content of the book was the motive that propelled them, characterizing the activity as such (^{LEONTIEV, 2010}).

In the first situation, reading the book is not constituted as an activity because what it was directed toward did not coincide with what motivated the student to read. Thus, in the first case, the activity consisted only of preparing the student for the exam, with reading the book being an action. As emphasized by ^{Leontiev (2010}, p. 69), "the goal of an action, by itself, does not stimulate the action."

In the second case, the student's continuation of reading suggests the need to know and understand the content of the book, transforming their reading into an activity with specific goals. This occurs because a new need of the student is satisfied with the understanding of the content, which goes beyond mere assimilation necessary for exam success. Based on this example, emotions and feelings are emphasized as important psychological aspects that are specially related to activity in its course (^{LEONTIEV, 2010}).

The transition from a principal activity to another, that is, from one stage of psychic development to another, occurs when the motive of the activity becomes the target of the action - in this case, when the appropriation of the content becomes more important than just passing an exam. "This is how all activities and new relationships with reality emerge" (^{LEONTIEV, 2010}, p. 69).

The question that arises from it is: how does the transition of motives guiding individuals' activities occur? At this point, Leontiev introduces the understanding of the genesis of motives, termed as motives that are only understandable, according to the first exemplified case, and truly effective motives, according to the second case. It is the latter that introduces the child to a qualitatively new social situation, different from the previous one. At this point in development, there is "a new objectification of their needs, which means they are understood at a higher level" (^{LEONTIEV, 2010}, p. 71).

Thus, we arrive at the explanation of the fundamental law of the dynamics of ages. According to this law, the forces propelling the child's development in each age ultimately deny and destroy the very basis of that age's development, internally and necessarily determining the end of the social situation of development, the end of a specific developmental stage, and the transition to the next one, that is, to a higher age period (^{VYGOTSKI, 1996}, p. 264, our translation). These conceptions guide us to investigate and understand the essential periods that constitute the periodization of psychical development, framed by the educational processes experienced by individuals in relation to others who are more developed.

3 General Characteristics of Human Psychic Development and the Role of School Education

The studies conducted so far highlight that the knowledge about psychic development involves, firstly, a historical focus on the rhythms of development and issues related to the emergence of certain periods throughout human historical development. Secondly, an approach that encompasses the individual's position in the system of social relations throughout the entire process. Thirdly, a conception that psychic development is a dialectically contradictory process, with interruptions caused by neo-formations. Fourthly, the differentiation of critical points in development are highlighted, which are important objective indicators of the transition from one period to another. Finally, the differentiation of turning points in each of the periods (^{ELKONIN, 1987}).

This leads us to the assumption that understanding psychic development cannot be achieved without an in-depth investigation of the objective aspect of the content of activity - that is, which aspects of reality the individual relates to in an activity and, consequently, to which aspects of reality they are oriented (^{ELKONIN, 1987}; ^{LEONTIEV, 1978}, ²⁰¹⁰; ^{VIGOTSKI, 1996}).

Thus, the analysis of psychic development consists of recognizing two main systems. The first concerns the system of child-adult social relations, in which activities involving orientation towards the fundamental senses of human activity and the assimilation of its goals, motives, and governing norms predominate (^{ELKONIN, 1987}).

These activities can be summarized as (i) direct emotional communication,

(ii) social role-playing games, and (iii) intimate personal communication, which substantially differ in their concrete content and the depth to which individuals penetrate the sphere of goals and motives of adult-performed activities. However, these activities share a common fundamental content, prevailing in the development of the motivational sphere and human-generic needs, that is, produced within society (^{ELKONIN, 1987}).

The second system is characterized by the child-object social relationship. In this system, activities involve the appropriation of socially elaborated and incorporated procedures as latent properties in objects, a result of collective human work. The different types of activities that make up this system are identified as

(i) object-manipulative activity, (ii) study activity, and (iii) study activity oriented towards productive work (^{ELKONIN, 1987}).

The theoretical and practical importance attributed to the hypotheses elaborated on the periodic nature of psychic development, based on the structuring of the periodization system according to ^{Elkonin (1987}), lies precisely in the possibility of overcoming the problems and concerns existing in child psychology. The development of motives and intellectual needs, called superior needs, reveals their unity with the development of individuals' personalities. This allows understanding their course in an ascending spiral scheme, not in a linear and parallel manner, as will be presented below 2(^{ELKONIN, 1987}).

Source: Own authorship, 2023.

Figure 1 Systematization of the periodization scheme based on ^{Elkonin (1987}). 

Having said that, in order to address the relationship between the development of higher psychic functions, human characteristics, and school education, Vygotsky (¹⁹⁹⁶) discusses the importance of analyzing the levels of development in which the individual finds themselves. According to the author, the analysis process involves understanding the sense and meaning of changes identified during and between such periods.

Therefore, the level of achieved development is determined by all of the activities the child can perform by themselves, without the assistance of an adult. On the other hand, the level of proximal development is defined by tasks that require collaboration and guidance from an adult - activities the child cannot perform alone but will be able to accomplish without assistance in the future (^{VYGOTSKY, 1996}).

The development of individual characteristics, that is, the personality of individuals, occurs through the interaction between the more developed being (adult) and the developing being (child). At this point, the practical significance of development analysis for school education is circumscribed (^{VYGOTSKY, 1996}).

Educational processes cannot be based solely on students' every-day and spontaneous activities. On the contrary, their planning requires the identification of the achieved and proximal development levels of students, as well as the essential and systematized knowledge necessary for all individuals to humanize themselves, without exception.

As highlighted by Vygotsky (²⁰⁰¹, p. 332), "every object of school learning is always built on a ground that is not yet matured," and it is only at the boundaries between both levels that learning becomes fruitful.

It is the teacher's responsibility to take as a guiding aspect of their practice not the least effort the child can offer to avoid "difficult" situations, leaving them to the whims of spontaneity, for instance, or offering knowledge they already master. Instead, the teacher should provide mediations with what is presented as proximal, potential, to be developed. It is at this point that school education influences the substantial changes that constitute, especially, the evolution and revolution between developmental periods.

Therefore, mastering the central concepts inherent to the knowledge about individual development periods, as well as the analysis between achieved and proximal development levels, stands as a sine qua non condition for the educational work of teachers inserted in school education, especially those dedicated to the development of a pedagogical practice that seeks to promote the full realization of human capacities and potentialities in all individuals.

4 Final Considerations

Understanding the central concepts regarding the relationship between the development of human psyche and school education, based on the theoretical- methodological assumptions of the Historical-Cultural Theory, is essential for those advocating a pedagogical practice that promotes development based on the maximum capacities and potentialities of all singular individuals.

As ^{Davidov (1988}, p.58) states, quoting Rubinstein's understanding of the relationship between psychology and pedagogy, "[... the object of psychology is characterized by the laws of the development of the child's psyche; from this perspective, the pedagogical process is its condition." On the other hand, "[... the object of pedagogy is characterized by the specific laws of education and teaching," with psychological development, in turn, being its condition. Therefore, the knowledge of the periodization of human development by the teacher, as well as the analysis of actual and proximal development levels, is fundamental for their pedagogical process.

By understanding the periods and milestones of child development, teacher is able to organize and execute educational practices according to the needs and capacities of the students. This understanding enables the creation of suitable, challenging, and meaningful learning situations that promote the advancement and integral growth of each child. Additionally, by considering each student's level of proximal development, teacher can identify the capacities and knowledge that are about to be developed and provide the necessary mediation for the effective learning takes place. Thus, knowledge of the periodization of human development becomes a valuable pedagogical instrument, allowing the teacher to guide and stimulate the educational progress of their students in a more effective and humanizing direction.

Therefore, a truly humanizing school education has the role of constructing pedagogical processes based on systematized knowledge, taking into consideration the social development situation of the students. These processes should be grounded in the understanding of main activities, based on critical studies of the periodization of psychological development, and structured based on the dialectic between proximal and achieved levels of development. Thus, they contribute to developing, in each singular individual, their maximum human potentialities, considering the specific period of their development. Therefore, by adopting a critical psychological approach to understanding human development, teachers have the possibility to promote an education that respects and values the individual characteristics of each student, fostering the flourishing of their capacities and enabling full and meaningful growth.