The "Pre-K Classroom Assessment Scoring System" (CLASS) is commonly used to measure three domains of teacher-child interactional quality in preschool classrooms (Emotional Support, Classroom Organization, and Instructional Support). However, there is considerable debate regarding the validity of its three-domain factor structure and the applicability of CLASS across different countries and educational settings. This study contributes to this debate with an investigation of the factor structure of the CLASS in Singapore, comparing the factor structure for preschool classrooms serving typically developing children (n = 184) and early intervention classrooms serving children who require early intervention support (n = 182). Bifactor measurement models were used to explore the dimensionality of the CLASS in these settings. A best-fitting bifactor model with one general (Responsive Teaching) and two specific factors (Proactive Management and Routines, Cognitive Facilitation) was a good fit for the overall data. Comparison of preschool and early intervention classrooms indicated partial metric invariance, suggesting that while the factor structure was equivalent across the different settings, the loadings on some dimensions differed between preschool and early intervention classrooms. Future research could examine how different aspects of interactions in different settings contribute to children's learning.