In this multimethod, multiagent longitudinal study, boys' dominance was studied as they made the transition from primary to middle school. A cohort of boys was followed as they moved from fifth grade (mean age 10.1 years of age) through sixth grade (mean age 12.1 years of age). Consistent with theory, dominance decreased as boys made the transition to a new group; aggression initially increased from primary school to the start of sixth grade and then decreased again at the end of the year. Additionally, and consistent with theory, dominance had a significant aggressive, but not affiliative, dimension at the start of sixth grade. By the end of the year, dominance did not have a significant aggressive dimension but did have a significant affiliative dimension. Last, both affiliative and aggressive dimensions of dominance predicted heterosexual relationships (i.e., dating) at the end of the sixth grade. Results are discussed in terms of distal, evolutionary effects and proximal, peer group effects on peer relations in adolescence.