The purpose of this study was to examine the relationship between language skills and behavioural problems and the potential moderating role of the quality of classroom emotional support in this relationship among 242 preschool children from low-income families. The Preschool Language Scale-5 was administered individually to each child. The quality of classroom emotional support was measured using the Emotional Support domain of the Classroom Assessment Scoring System for Pre-Kindergarten. Teachers and parents completed the Child Behaviour Checklist for Ages 1½–5. Results indicated the inverse relationship between language skills and behaviour problems varied by the level of classroom emotional support provided by teachers. Specifically, children with lower language skills exhibited higher levels of behaviour problems in classrooms where teachers provided lower levels of emotional support. Findings from this study have important implications for enhancing teachers’ emotional support aimed at children with lower language skills and for future research. (author abstract)