The assessment of children's social skills is an important task for school psychologists in both applied and research settings. The present study examines the psychometric properties of parent ratings of the Social Skills Rating System (SSRS), in kindergarten through third grades, testing for measurement differences between boys and girls, between African American, Caucasian, and Hispanic children, and across time from kindergarten through third grades. The analyses used a longitudinal sample of 4345 children from over 600 schools in 30 states to examine these questions using multigroup confirmatory factor analysis. Results provide qualified support for the use of the SSRS for kindergarten through 3rd-grade students across these different populations. However, if scored according to the manual, these results indicate that the measure may not be assessing the same construct over time or for all ethnic groups. If corrections to the factor structure and scoring system are incorporated, these results provide a basis for using parent ratings of the SSRS to assess social skills and problem behaviors across time, ethnicity, and sex in early elementary school.