This study evaluates how teacher report measures align with different conceptualizations of children's social-emotional development. Leveraging seven teacher report measures of social competence and behavioral regulation in a predominantly low-income, population-based rural sample of four-year-old children (n = 828), model fit and validity were evaluated in a series of confirmatory factor models, including bifactor models. A bifactor model with behavioral regulation as a general factor and an orthogonal social competence factor emerged as the preferred model. Results indicate that teacher reports of behavioral regulation capture teachers' perceptions of preschoolers' behavioral regulation. However, teacher reports of social competence reflect teachers' perceptions of both social competence and behavioral regulation. Post-hoc analyses were conducted to explore potential explanations for these findings. Implications for interpreting teacher reports of social-emotional development and for future work strengthening the quality of scalable measures of children's social-emotional development are discussed. [Cowritten with The Family Life Project Key Investigators. This paper was published in "Early Childhood Research Quarterly" v48 p98-110 2019.]