In the framework of the Cultural-Historical Activity Theory (CHAT) the leading activity is the activity, or cooperative human action, which plays the most essential role in child development during a given developmental period. Although many activities may play a role in a child's development at any given time, the leading activity is theorized to be the type of social interaction that is most beneficial in terms of producing major developmental accomplishments, and preparing the child for the next period of development. Through engaging in leading activities, a child develops a wide range of capabilities, including emotional connection with others, motivation to engage in more complex social activities, the creation of new cognitive abilities, and the restructuring of old ones (Bodrova & Leong 2007: 98).
The term "leading activity" was first used by Lev Vygotsky (1967: 15–17) in describing sociodramatic play as the leading activity and source of development of preschoolers, but it was not systematically incorporated into Vygotsky's theory of child development. Later, however, Alexei Leontiev and other "neo-Vygotskians" such as Alexander Zaporozhets and Daniel Elkonin (Zaporozhets 1997; Zaporozhets & Elkonin 1971) made the concept a fundamental element of their activity theory of child development. The concept has now been extended to several stages or periods in human development.
The notion of a the leading activity is part of a broader theory of activity that attempts to integrate cognitive, motivational, and social aspects of development. Despite many detailed descriptive accounts of the developmental forms of memory, perception, and cognition in various phases of childhood (e.g. Piaget's work), often missing is an explanation for how or why the child develops these psychological processes (Karpov 2003: 138). The exploration of leading activities seeks to illuminate these questions. Rather than biological maturation or stimulus-response learning, specific types of social activity are seen as generating human development. Because of its attention to causal dynamics, the neo-Vygotskian theory has been called "the most comprehensive approach to the problem of determinants and mechanisms of child development (Karpov 2003: 138)."
Nature A leading activity is conceptualized as joint, social action with adults and/or peers that is oriented toward the external world. In the course of the leading activity, children develop new mental processes and motivations, which "outgrow" their current activity and provide the basis for the transition to a new leading activity (Kozulin, Gindis, Ageyev, & Miller 2003: 7). In most cases, the emergence of an activity can be seen long before it becomes the leading activity in a child's life (Bodrova & Leong 2007: 99). Adults and more capable peers who instruct or assist children in engaging in the leading activity are said to be providing mediation of the activity, and creating a zone of proximal development, which allows children to perform activities at a higher level than they could perform independently. Mediation of leading activities is theorized to help children develop by acquiring the use of cultural or psychological "tools," which transform children's mental processes.
Sequence The activity considered leading for any given age or period of development depends on the type of society in which a child develops, and on the particular historical and cultural expectations for children of that age (Bodrova & Leong 2007). Neo-Vygotskians have proposed a sequence of children's optimal leading activities in modern industrialized societies (though leading activities may differ in agrarian or hunter-gatherer societies). Of course, not all children within a particular culture will engage equally in leading activities (or in equal "quality" of activities), which leads to different developmental trajectories and outcomes. For example, children who lack opportunities to engage in rich, well-developed sociodramatic play during their preschool years appear to have greater difficulty with self-regulation and impulse control, characteristics associated with the diagnosis of attention deficit hyperactivity disorder (ADHD) (Bodrova & Leong 2007: 99)
The proposed sequence of leading activities is not strictly determined by biological age, but rather by the typical age-related forms of adult and peer interaction in a given society (Chaiklin 2003: 48). As a result of their historical and cultural specificity, leading activities are subject to change. Different leading activities may develop and be found more beneficial for development within particular societies, leading to a revision or reconceptualization of the most effective leading activities. Karpov (2005) reviews recent empirical findings of Western researchers, which are highly consistent with the neo-Vygotskian analysis of child development through engagement in leading activities.
Infancy: emotional communication with caregivers During the first year of life, emotional communication with caregivers is seen as the leading activity and context in which the developmental achievements of infancy occur. Vygotsky saw these interactions as the social foundation that would lead to learning and development in a uniquely human way (Karpov 2005). Primary caregivers establish an emotional dialogue with infants that goes beyond mere diapering and feeding routines. Development of this active, two-way emotional relationship results in what Bowlby (1969) called attachment. This shared activity is the blueprint for future relationships the child will develop, and creates motivation for the child to engage in later forms of shared activity (Leontiev 1978).
Infants' emotional exchanges with caregivers begin with purely emotional exchanges, such as smiling or cooing back and forth, or more physical interactions such as when a baby happily responds to hugging, bouncing, or tickling (Bodrova & Leong 2007). Caregivers generally take the initiative in establishing emotional rapport with infants, and infants move from being relatively passive participants to taking increasingly active roles in these dialogues. It has been found that around the beginning of the second month of life, infants begin smiling in response to their caregivers' smile and voice (Zaporozhets & Markova 1983).
In the third month of life, children begin smiling, gesturing and vocalizing (cooing) when greeting familiar adults. Vygotskians have called this the animation complex and infants soon come to use it proactively to arouse and maintain the attention of a caregiver (Bodrova & Leong 2007). From around three to six months of age, infants use smiles and vocalizations to invite caregivers to engage in emotional exchanges, creating what researchers such as Tronick have called interactional synchrony (Tronick 1989). Parents often use "baby-talk" or "child-directed speech" in response to their children's prelinguistic vocalization (e.g. babbling), and it has been shown that infants respond by modifying their babbling in accordance with the phonological structure present in their caregivers' utterances (Goldstein & Schwade 2008). This sort of vocalized emotional interaction, or what John Locke (2001) has referred to as vocal communion, appears to be linked to attachment and later lexical learning, thus playing a formative role in language development.
During the second half of the first year of life, infant-caregiver interactions expand to include emotional exchanges around objects, and actions on those objects (Bodrova & Leong 2007). For instance, a father may now smile and shake a rattle in response to the baby's smile. Around this time, parents may begin to label objects and talk about the actions they are performing. For infants, these objects become interesting as they are presented through emotional interaction with adults (Karpov 2005). While Piaget believed that infants' sensorimotor manipulation of objects came through spontaneous body movements and exploratory actions, evidence suggests otherwise. Children who were severely deprived of emotional contact did not engage in much object manipulation, even though objects were accessible to them in their cribs (Lisina 1974; Spitz 1946). This supports the Vygotskian assertion of a link between emotional interactions with caregivers and the development of object manipulation and exploratory behavior.
In this new context of emotional communication around objects, infants develop more sophisticated communication tools of gestures and words. Vygotsky (1988) describes how an infant's unsuccessful grasping for an object is assigned social meaning when an adult hands the object to the child. The grasping motion then transforms into pointing, an instrumental gesture communicating to an adult the baby's desire, and perhaps prompting the adult to act on the infant's behalf (Vygotsky 1988). Like gestures, a child's first words are treated as meaningful by the adults, and only later are used by infants to signify objects, people, and actions (Bodrova 2007: 104). A baby may make a random "da da" sound in her father's presence, and happy parents assign these sounds the meaning "Daddy," a meaning which the baby then learns from the parents. Language thus emerges in shared form, with adults initially providing most of the verbal interaction, and children eventually beginning to appropriate and use the tool of language themselves (Bodrova & Leong 2007: 104).
In summary, a positive emotional attitude toward adults is crucial for infants' development, as it leads to a vital interest in what the adult presents to the infant and does in their presence, such as using language and manipulating cultural objects, such as toys (as opposed to mere "natural" objects, such as rocks). As Yuri Karpov (2003: 142) put it, "Figuratively speaking, infants become interested in the external world because it has been presented to them by loved adults." Infants accept adults as mediators of their relations with the world, and show increasing interest in the actions they can perform with cultural tools and objects (Bodrova & Leong 2007). This leads to infants' transition to a new leading activity.
Toddlerhood: object-centered joint activity Although infants begin to engage in object manipulations during the first year of life, the nature of these manipulations changes qualitatively during the second year of life, when object-centered joint activity with adults becomes toddlers' leading activity. Though for much of infancy children have been involved with "dyadic" interactions with caregivers, or independent interactions with objects around them, around this time toddlers become centrally engaged in actions that are "triadic" in the sense that they involve the child, the adult, and some object or entity to which they share attention (Tomasello 1999). While working with objects toddlers look where their caregivers look (gaze following), use adults as social reference points (social referencing), and act on objects the way adults act on them (imitative learning) (Tomasello 1999). Toddlers tune into the ways adults are using objects, and use communicative gestures to get adults to tune into them, as well as objects in which they are interested.