In the present study, essentially we examined the sex-related reciprocal effects (or covariance structure) among math achievements (i.e., standardized test-scores and teacher-assigned grades), self-concept, and interest from Grade 5 to 7. More specifically, we used cross-lagged panel analyses across sex groups to study the interplay of both self-concept and interest and achievement. Besides, we extended the examination of sex differences beyond the bivariate relations to the latent mean structure of these constructs and described their trajectories.