Discrepancies among informants’ ratings of a given child's behavior complicate the study of linkages between child behavior and academic achievement. In the current study, we examined the potential moderating effect of informant type on associations between behavior and two types of achievement in a longitudinal growth model that captured children's development from 54 months of age through fifth grade. Latent internalizing and externalizing behavioral constructs, as separately measured by mothers and teachers, were modeled as time‐varying predictors of achievements to capture changes that occur as children progress through different developmental stages. Behavioral ratings obtained by both informants explained largely equivalent levels of reading achievement variance, and teachers’ ratings of child behavior explained more variance in analytic type achievements than did those of mothers.