Research Findings: Child temperament is an important construct, but its measurement has been marked by a number of weaknesses that have diminished the frequency with which it is assessed in practice. We address this problem by presenting the results of a quantitative construct validation study. We calculated validity indices by hypothesizing the magnitude of relationships between Behavioral Style Questionnaire (BSQ) subscales and criterion measures assessing student-teacher relationships, student characteristics related to teaching stress, and peer play interactions. We tested these hypotheses against the actual correlations observed in a sample of 44 children 40 to 68 months of age. These analyses indicated strong support for 4 of the BSQ subscales (Activity, Rhythmicity, Approach, and Adaptability) and moderate support for 1 subscale (Mood). However, new item generation and testing is recommended for 3 subscales (Intensity, Persistence, and Threshold), along with further construct definition work for the final subscale (Distractibility). Practice or Policy: These findings are particularly relevant for early childhood educators who wish to assess temperament yet are uncertain of the issues involved in its measurement. Results derived from the BSQ, viewed in context, can increase practitioners' understandings of children's individual characteristics and guide the development of interventions to promote optimal early educational experiences for children.