Peer groups are a powerful part of young people's lives. As the first step in investigating the potential of peers as developmental resources or liabilities during the normatively stressful transition to high school, the purpose of this study was to identify and measure the features of peer relationships that shape healthy development, and the contextual conditions that promote them. The Friendship Group Motivational System (FGMS) is a new conceptualization that includes two individual level concepts (friendship group interactions and self-system processes), and an emergent motivational group-level concept (friendship group engagement and disaffection).

Items were developed to measure the 13 constructs making up the three core FGMS concepts. A sample of 443 freshman students completed a battery of questionnaires, including the FGMS construct items. Participants were also asked to nominate their ninth grade school friends; the reciprocated nominations were used to calculate composite group profile scores for friendship group engagement and disaffection.

In a series of confirmatory factor analyses, nine of the 13 FGMS constructs were successfully derived and replicated. Dimensionality analyses revealed that many of the FGMS measures were not sufficiently distinct. The extent to which individuals and their reciprocally nominated friends agreed on their friendship group engagement and disaffection varied a great deal. Nevertheless, all of the new measures functioned well. All 13 FGMS constructs were related to similar measures, which is evidence of construct validity. Although the measures were differentially reliable for subgroups of adolescents, all of the within- and between-construct relationships occurred as hypothesized. The unique relationships found between the three FGMS concepts suggest that individual and group processes should be conceptualized and measured separately. The FGMS constructs were also related to indicators of high school transition stress, academic engagement, and personal and social adjustment.

This research makes a significant contribution to the peer relations field by positing specific ways in which friendship groups support or undermine adolescents' healthy functioning, and by providing new tools for testing these relationships. The FGMS model can be used to explain the relationship between peer groups and long term development, to examine how peers influence individual coping, and to develop new school-based interventions.