The goal of this study was to examine links between observed social participation in the schoolyard and indices of socio-emotional functioning in early adolescence. Participants were children (N = 290) aged 9 to 12 years. Social participation (e.g., solitary play, dyadic interaction, group interaction) was assessed in the schoolyard during recess and lunch using behavioral observations. Measures of perceptions of peer difficulties (e.g., perceived peer relations, loneliness) and internalizing problems (e.g., social anxiety, depression) were provided via maternal ratings and child self-reports. Results from cluster analyses revealed several subgroups of children characterized by distinct patterns of social participation. The groups also differed in terms of their socio-emotional functioning. For example, nonsocial children (who displayed the most frequent solitary activities) reported the highest levels of internalizing problems and more peer difficulties. Results are discussed in terms of the utility of observed social participation behaviors as marker variables for socio-emotional difficulties in early adolescence.