The purpose of this study is to examine the bidirectional relationship between children’s language development and challenging behaviors as well as the moderating roles of gender and race/ethnicity. We conducted a number of structural equation modeling analyses with a national representative sample (N = 2,462) of Head Start children from the 2014 Head Start Family and Child Experiences Survey. Results suggest that there is no bidirectional relationship between vocabulary development and challenging behavior in the full sample. However, gender, race/ethnicity, and the interaction between the two moderate associations between language and behavior. (author abstract)