Background: The idea that screens 'stole children's focus' and that reading books, in contrast, stimulates selective attention is theoretically complex and has largely been ignored in empirical tests. Research has identified positive associations between reading habits and various dimensions of attention in children, but most research is restricted to book or print reading habits, with limited evidence for digital habits. Methods: We tested the assumption that selective attention (students' ability to focus on relevant information and to ignore distractors) may mediate the relation between print and digital reading habits and comprehension in a longitudinal study that analysed 654 fourth and 635 fifth grade students at the end of their school year (T1) and 1 year later (T2). Results: Overall, and contrary to our expectations, the longitudinal associations for reading habits in T1 to selective attention and reading comprehension in T2 were mostly null. Digital reading habits for academic purposes in T1 were negatively associated with reading comprehension in T2, for students assessed from 4th to 5th grade, but not those from 5th to 6th grade. In addition, students' selective attention was positively associated with reading comprehension. Conclusions: To conclude, we discuss the need to search for mediators other than selective attention on the associations between reading habits and comprehension and highlight the need to identify key developmental milestones during primary school that may be accomplished to be ready to take full advantage of digital reading practices.