Educational apps can help children develop their early numeracy skills, but only if they incorporate certain pedagogical features. AppLINOU is an early numeracy app that was co-designed by a multidisciplinary team to be compatible with the way numeracy is taught in France's preschools. This study of whether incorporating AppLINOU into classroom teaching has a beneficial effect on students' early numeracy skills is the first quasi-experimental study of an educational app to be conducted in France's preschools. The study included 537 preschool students (mean age 4.42) followed up to first grade (mean age 6.32). Students in the experimental group (n = 345) used AppLINOU during their lessons to practice ten numeracy activities over 25 weeks. Students in the control group (n = 192) did not use AppLINOU. Both groups of students followed the same syllabus. Multilevel growth models show that students in the experimental group had progressed more by the end of the experiment than those in the control group.