Although the acceptance of educational apps and their contributions to learning have been widely researched, none of these studies have examined links between teachers' acceptance of apps and their students' skills. The present study investigated this issue with respect to a new, French-language educational app for helping preschool children improve their early literacy and early numeracy skills. To this end, we measured the app's acceptance by 33 French preschool (école maternelle) teachers, who used it in class for ten weeks, and the early literacy and early numeracy skills of their 353 students (aged between 3.92 and 4.91 years). Multilevel regression analyses revealed a significant link between the students' post-test early literacy and early numeracy scores and their teachers' perception of the app's usability. These results show that taking teachers' acceptance into account is an interesting opportunity to better understand the potential effectiveness of educational apps in school settings. Implications for teachers' training are also discussed.