The objective of this study was to examine the concurrent and longitudinal social and behavioral correlates of social network isolation and the patterns of isolation across the transition to middle school. It was hypothesized that students who were isolated from the social network would also have difficulties with aspects of school and social-emotional functioning, including teacher-rated internalizing and externalizing behavior, self-reported school belonging, peer-rated sociometric status (including social preference and social impact), and teacher-rated participation in friendships. It was further hypothesized that isolation would remain stable; students who were isolated at one time point would be more likely to be isolated at future time points than would students who were integrated into the social network. Students who were not members of social groups identified by the Social Cognitive Mapping Procedure were considered isolated from the social network, and were the focus of the current study. The results of this study indicated that isolated students were at increased risk of difficulty on measures of school functioning (internalizing behavior, externalizing behavior, and school belonging) at some time points around the middle school transition, but not at others. Students who were isolated from the social network had increased risk of difficulty on measures of social functioning (social preference, social impact, and friendships) at all three time points around the transition. In addition, the results of this study suggested that students who were isolated at one time point were more likely to remain isolated at future time points than would be expected by chance. Finally, the results of this study suggested that the experience of social isolation at one or more time points was significantly related to difficulties with school belonging after the transition, but not internalizing or externalizing behaviors, after controlling for initial levels of functioning. The results of this study suggest that the experience of social network isolation is related to some difficulties in concurrent and longitudinal functioning, and is related to increased risk of continued isolation. Limitations of the current study and implications for future research were discussed.