Children's expression and regulation of emotions are building blocks of their experiences in classrooms. Thus, the authors' primary goal was to investigate whether preschoolers' expression or ability to regulate emotions were associated with teachers' ratings of school adjustment. A secondary goal was to investigate how boys and girls differed across these associations. Children's social-emotional behaviors in Head Start and private childcare center classrooms were observed, and using a series of measures, teachers' ratings of children's social competence, attitudes toward school, positive teacher relationships, and cooperative participation were collected. Three factors of children's school adjustment were extracted from these indicators. A series of hierarchical regressions revealed that emotion expression and regulation were indeed associated with children's reported school adjustment, with the strongest associations stemming from children's negative emotion expression and their emotion dysregulation. Many of these associations were also different for boys and girls. The results corroborate and extend the authors' earlier findings, and have implications for social-emotional programming to maximize children's early school success. (author abstract)