Academic language and its associations with school success have been established in many prior studies. However, the scholarship lacks research on the mechanisms that constitute these relations. This study investigates the mediating role of motivational-­affective variables, specifically reading self-concept and reading enjoyment, in relations between academic language and reading comprehension assessed one year later. Path analyses were performed with a newly developed German measure of academic language proficiency on two samples (N = 198, M[subscript age] = 9.05 years [SD = 0.76], 49% girls, and N = 360, M[subscript age] = 9 years [SD = 0.80], 52% girls) of primary school students in Grades 2 and 3. Results reveal differential outcomes, suggesting an effect mediated via reading self-concept when academic language is operationalized as the comprehension of connectives. The findings are discussed within the context of contemporary perspectives on mental abilities, ranging academic language into current views on cognitive capabilities.