Reading self-concept is an important predictor of reading comprehension and vice versa. However, the mechanisms that are at work in this relation have yet to be identified. In line with the self-enhancement approach, we propose that in the reading domain, amount of reading, book choice (text difficulty and book length), and intrinsic reading motivation should function as mediating variables in the relation between reading self-concept and reading comprehension. We tested this hypothesis with longitudinal data gathered from N = 405 German students in Grades 7, 8, and 9. The results showed that reading self-concept had a positive effect on reading comprehension, intrinsic motivation, book length, and amount of reading. However, indirect paths between reading self-concept and reading comprehension were found only for intrinsic motivation, not for amount of reading or book choice. The results are discussed in the context of students' reading comprehension development, and consequences for research and education are derived.