School structure explains age group differences in friend selection similarity

The present study tests the hypothesis that friend selection similarity increases after the transition into middle school but only for those attending schools with an expanded pool of similar others who could potentially serve as friends. Participants included 456 (247 girls, 209 boys) students (ages 10–15) attending public primary and middle schools in Florida (USA) and Lithuania. In Florida, 40.2% were European American, 26.5% were Hispanic-American, 22.6% were African American; the remainder had other backgrounds. Most Lithuania students were ethnic Lithuanian. Florida and Lithuania primary school students attended classes with the same 22–24 classmates. Florida middle school students attended classes with a rotating group of students, drawn from 78 to 89 potential classmates. Lithuania middle school students attended classes with the same 21–30 classmates. Participants completed peer nomination surveys twice during a single academic year, from which 344 (Florida n = 168, Lithuania n = 176) future-friend dyads [i.e., partners who reciprocally nominated one another as friends in January (Time 2) but not in September/November (Time 1)] were identified. Within-dyad intraclass partial correlations indicated that Florida middle school future friends were more similar than primary school future friends on peer-reported academic achievement, acceptance, athleticism, and popularity (but not on disruptiveness or rejection). In Lithuania, there were no differences between primary school and middle school future-friend similarity. The findings suggest that previously identified developmental increases in friend similarity can be traced, in part, to structural changes in schools, such that middle schools with rotating class rosters provide students with more options to identify compatible others than primary schools.