From the New York Times:

“In middle childhood, the brain is at its peak for learning, organized enough to attempt mastery yet still fluid, elastic, neuronally gymnastic. Children have lost the clumsiness of toddlerhood and can become physically gymnastic, too, and start practicing their fine motor skills. And because they are still smaller than adults, they can grow adept at a skill like, say, spear-tossing, without fear of threatening the resident men.

Middle childhood is the time to make sense and make friends. “This is the period when kids move out of the family context and into the neighborhood context,” Dr. Campbell said.

The all-important theory of mind arises: the awareness that other people have minds, plans and desires of their own. Children become obsessed with social groups and divide along gender lines, girls playing with girls, boys with boys. They have an avid appetite for learning the local social rules, whether of games, slang, style or behavior. They are keenly attuned to questions of fairness and justice and instantly notice those grabbing more than their share.”

Thanks to Sara, for bringing this to our attention.