By focusing on the domains of math and German, the present study with 200 elementary school children investigated the specific relationships of self-reported grades with academic self-concepts and self-perceptions of effort within the competence-affective separation of academic self-concepts. In addition, possible mediator effects of academic self-concepts were explored. In both domains, self-reported grades positively predicted academic self-concepts of corresponding domains, which, in turn, positively predicted self-perceptions of effort of corresponding domains. However, there were no negative cross-domain achievement effects on academic self-concepts and no negative cross-domain self-concept effects on self-perceptions of effort. Both academic self-concepts mediated the effects from self-reported grades to self-perceptions of effort in corresponding domains. This research indicates that children’s self-perceptions of effort can be inferred by their competence and affective self-concepts.Highlights Self-reported grades positively predict academic self-concepts of corresponding domains. Academic self-concepts positively predict self-perceptions of effort of corresponding domains. There are no negative cross-domain achievement effects on academic self-concepts and no cross-domain self-concept effects on self-perceptions of effort. Academic self-concepts mediate the effects from self-reported grades to self-perceptions of effort in corresponding domains.