Professor Doris Bergen of Miami University distinguishes play from other childhood activities by noting that it is self-chosen and not geared toward an end result. The child feels a measure of "personal inner control," able to bend and shape and invent reality at will. Motivation to play must come from within, arising spontaneously, rather than in response to an external command. Though it's not measurable by science, the most crucial aspect of developmental play is "fun."
In the first three years of life, the 100 billion neurons in a child's brain are rapidly forming links. Brain development is characterized by rapid periods of chaotic growth interspersed with restive periods, in which the brain assimilates and organizes information. According to Bergen, children "grow their own brains" as their play experiences simultaneously activate areas of the brain and influence the organization of neural pathways. Toddlers have twice the density of brain synapses that adults have. "Pruning"--sheering away unused neural connections--is necessary to make the brain work faster and more efficiently. Play reinforces necessary connections, ensuring they aren't "pruned" away.
Some researchers--B.F Skinner and Jerome Bruner, for example--emphasize the external component of language development, suggesting that the process mostly involves using information gleaned from past experiences to understand and incorporate current external stimuli. Jean Piaget and Noam Chomsky place more importance on internal forces. Their theories essentially suggest that children's brains have built-in knowledge--pre-existing templates for language. Regardless of whether external or internal forces are dominant, however, all the research indicates that play is a vital factor in language development.
According to University of California Psychology Professor Susan Ervin-Tripp, children do a better job of teaching each other language through play than adults do when they provide didactic instruction. Through role play and fantasy games, or even in arguments about toys or the rules of a game, children develop a strong internal motivation to develop language so that they can express themselves effectively. They naturally exchange vocabulary through role play games that involve imitating adults. A child introduces words he has learned from the adults in his home to a child who has not learned those words.
Bergen urges policy makers to consider the importance of play in language development when they determine the curricula for preschools and kindergartens. Because U.S. educators place high value on test scores, they have scaled back or eliminated recess time and other free-form activities in favor of programs designed to promote "academic readiness." But research suggests that play in the formative years makes children far more academically "ready" later in life.