The Boston College research psychologist says that his work - most of which has been carried out in a school in Massachusetts - has convinced him that age-mixed play has many advantages over age-graded play.

The Massachusetts school, Sudbury Valley, does not assign students to grades or classrooms. Instead, it allows them to go wherever they wish in the school buildings and campus, and to interact with whom they please. Their education is entirely self-directed. Daniel Greenberg, one of the school’s founders and the leading exponent of its philosophy, contends that the key to the school’s educational success is free age-mixing.

One advantage observed by Prof Gray for the younger participants in age-mixed play is that it allows them to engage in, and learn from, activities that they could not do alone or just with other children of the same age.

For example, two 4-year-olds cannot play a game of catch together. Neither can throw the ball straight enough or catch well enough to make the game work. But a 4-year-old and a 9-year-old can play and enjoy such a game. The 9-year-old can toss the ball gently into the hands of the 4-year-old and can leap and dive to catch the other’s wild throws.

In the same way, under-nines generally cannot play formal card games together. They lose track of rules, their attention wanders, the game quickly disintegrates. But at Sudbury Valley, children younger than this play cards with older children or adolescents. The older players remind the younger ones what they have to do.

“Hold your cards up so others can’t see them.”

“Pay attention to the cards already played and try to remember them.”

Gray says the reminders are given just when necessary, to keep the game going and to keep it fun for all. In the process, the younger children become better at paying attention, keeping track of information, and thinking ahead.

These are the foundation skills that underlie what we commonly call intelligence.

"Similar suggestions and boosts occur in all sorts of age-mixed games - computer games, writing games, outdoor games, informal fantasy games, and rough-and-tumble play. In the name of fun, the older participants naturally, and often unconsciously, erect scaffolds that allow younger ones to stretch and build their physical, social, and intellectual skills.

"Motivation is no problem in such learning. All of the children are playing because they want to, and they all strive to play well. Many children at Sudbury Valley have learned to read and write, without formal instruction, solely through the scaffolding provided by their playmates," Gray writes.

The benefits of age-mixed play go in both directions, according to the Boston College research professor. In interactions with younger ones, older children exercise their nurturing instincts and take pride in being the mature person in a relationship. They also consolidate and expand their own knowledge through teaching.

"When older children explain rules, strategies, moral principles, or other concepts to younger ones, they have to make their implicit understanding explicit, which may lead them to re-examine what they thought they already knew.

"Moreover, just as younger children are attracted to the more sophisticated activities of older ones, older children are attracted to the creative and imaginative activities of younger ones. At Sudbury Valley, we have frequently observed teenagers playing with paints, clay, or blocks, or playing make-believe games - activities that most teenagers elsewhere in our culture would have long since abandoned.

"In the process, the teenagers become wonderful artists, builders, storytellers, and creative thinkers."

In conclusion, Prof Gray urges a breakdown of the barriers which keep young people of different ages apart - a necessary step if we are to capitalize on children’s and adolescents’ natural, playful ways of learning.

"Age segregation deprives them not only of fun, but also of the opportunity to use fully their most powerful natural tools for learning." (Source: Education Week)