Evidence from ethnology, anthropology, and educational history and research indicates that age segregation is neither necessary nor natural. An examination of primate and simple human societies suggests that rigid assumptions about age segregation of the young is a recent departure from social patterns existing for millions of years. The researcher summarizes the findings of 27 empirical studies in multiage grouping in elementary schools conducted between 1948 and 1981 in the United States and Canada: multiage grouping has no consistent relationship with academic achievement, and multiage grouping has a generally benign effect on social and emotional development. Naturalistic and observational studies on companionship outside the classroom provide further evidence on the importance of cross-age grouping. The general pattern that emerges from these studies is one of increased competition and aggression within same-age groups and increased harmony and nurturance within more natural multiage learning groups where younger members seem to benefit most. Two tables provide statistics from empirical studies on multiage grouping. (PB)