Final answer:
Peer groups in middle childhood foster social development through interaction with children of similar age and status, promoting social skills and identity formation.
Step-by-step explanation:
In middle childhood, peer groups significantly contribute to social development by providing interaction with children of similar age and social status, rather than specifically with different ages, other races and social backgrounds, or the opposite sex. During this phase, peer groups offer the first major opportunity for socialization outside the family unit, which is crucial for identity formation and independence. Children in these groups engage in shared activities, support each other, and start to understand social roles and cooperation. As such, they learn valuable interpersonal skills and develop a sense of belonging through common interests.