The present study focused on students' academic enjoyment as predicted by achievement in multiple academic domains. Assumptions were based on Marsh's internal/external (I/E) frame of reference model and Pekrun's control-value theory of achievement emotions, and were tested in a sample of 1380 German students from grades 5 to 10. Students' academic enjoyment, self-concept, and achievement were assessed in relation to mathematics and verbal language classes. In line with assumptions of the I/E model, mathematics performance assessed in the previous academic year positively predicted enjoyment in mathematics classes, and negatively predicted enjoyment in language classes. Language class performance positively predicted enjoyment in language classes, and negatively predicted enjoyment in mathematics classes. Corroborating assumptions derived from Pekrun's control-value theory, achievement/enjoyment relations were mediated by academic self-concepts. Despite stereotypic gender differences in mean values, linkages between constructs were invariant across genders.