Accurate measurement of behavioral functioning is a cornerstone of research on disparities in child development. This study used the National Longitudinal Survey of Youth 1979 (NLSY79) data to test measurement invariance of the Behavior Problem Index (BPI) during middle childhood across three ethnic groups. Using the internalizing and externalizing behavior problem division derived by Parcel and Menaghan (1988) and suggested for use with NLSY79 data, the configural invariance hypothesis was not supported. The BPI factor structure model was revised based on theoretical considerations using the division of items from the Child Behavior Checklist. This model demonstrated configural invariance across ethnic groups and over time. Moreover, measurement invariance of factor loadings and thresholds across ethnic groups at each time point and within each ethnic group over time was also supported. The implications of these findings for educational and cross-cultural research are outlined. (Contains 6 tables.)