The goal of this study was to examine the potential linear and moderating effects of social anxiety and extracurricular activity participation in the prediction of young children’s early school adjustment. It was hypothesized that social anxiety would be harmful, and extracurricular activity participation would be beneficial for young children’s early school adjustment. Extracurricular activity participation was also expected to protect socially anxious children from negative school adjustment. Participants were N = 268 young children (aged 4-7 years) attending preschools and elementary schools located in south-eastern Ontario. Multisource assessment included parent, teacher, and child reports. Among the results: (1) social anxiety was associated with negative outcomes in early childhood; (2) engagement, but not frequency, of extracurricular activities was associated with early school adjustment; and (3) moderating effects of extracurricular activities were generally not found. Results are discussed in terms of implications for young socially anxious children’s positive early school adjustment.