Final answer:
The true statement about peer groups in middle/late childhood is that peers help children assess themselves by providing opportunities for social comparison.
Step-by-step explanation:
The correct statement about peer groups/interactions in middle/late childhood is 'D. Peers help children assess themselves more accurately by providing a social comparison.' This is because, as children progress through various stages of development, their interactions with peers play a significant role in their socialization process. Peer groups act as agents of socialization, where children learn to cooperate, share, and compare themselves to others. This is particularly true when they engage in various activities with peers versus family, thereby gaining an understanding of social norms and self. While preference for mixed-sex groups may emerge, the statement claiming children under 12 years of age prefer mixed-sex peer groups to same-sex peer groups is not universally true and depends on the child's personal development and social context.