The purpose of this mixed methods project was to investigate underactive behaviors in low-income, preschool children from an ethnically- and linguistically-diverse, largely immigrant sample. Two studies were conducted in order to meet this goal. The first study used quantitative methodologies to identify children engaging in at-risk levels of underactive behaviors in the classroom, as well as to examine the relationships between underactive behaviors in the classroom and school readiness outcomes. In addition, parents and classroom teachers reported on preschooler's peer play behaviors to assess the congruence of underactive behaviors in the play context across school and home. The second study used qualitative research methods to explore culturally-based beliefs and practices of parents (of underactive children identified in Study 1) related to underactive behaviors in early childhood. (author abstract)