Background: Mind wandering (MW) has commonly been linked to bad scholastic performance; however, such association has rarely been investigated in the classroom. Moreover, in examining such association, motivational variables have been largely ignored. Aim: We aimed at examining the associations between the dispositional tendency to engage in MW and a series of reading comprehension skills and measures of academic self-concept above and beyond the role of sex, age, test anxiety, self-efficacy, and self-regulation strategies. Sample: Late adolescents (N = 272, 133 females; 17.23 ± 1.10 years) recruited from 15 classes in public high schools. Methods: Students were examined in their classroom during regular teaching activities and first performed a reading comprehension test. Then, they underwent a battery assessing literacy skills, academic self-concept, the dispositional tendency to mind wander, and aspects related to self-regulated learning. Results: Reading comprehension and literacy skills (decoding, orthographic awareness, spelling skills, and phonological abilities) were not associated with the tendency to mind wander. Instead, MW, test anxiety, and self-efficacy -- but not self-regulatory strategies -- were independent predictors of academic self-concept. Conclusions: This study highlights the importance of evaluating the effects of MW on academic self-concept, taking into account a complex pattern of motivational and emotional variables.