A gender-labeling task was used to test the ability of 21 girls and 22 boys ranging in age from 21 to 40 mo to discriminate between pictures of boys and girls and male and female adults. Ss who passed the gender task (mean age 30 mo) were compared with Ss who failed it (mean age 26 mo) on 3 behaviors most often categorized as sex typed (toy choice, aggression, and peer playmate selection). It was predicted that Ss who passed the task would choose more sex-typed toys and same-sex peers and that there would be a drop in aggression for girls who passed but no change for boys. Results confirm the predictions for aggression and peer choice but not for toy choice. The relation between the child’s understanding of gender categories and environmental influences is discussed.