This study investigated the developmental trajectory of two marker effects of visual word recognition, word frequency, and orthographic neighbourhood effects, in French primary school children from Grades 1 to 5. Frequency and neighbourhood size were estimated using a realistic developmental database, which also allowed us to control for the effects of age-of-acquisition. A lexical decision task was used because the focus of this study was orthographic development. The results showed that frequency had clear effects that diminished with development, whereas orthographic neighbourhood had no significant influence at either grade. A self-organising neural network was trained on the realistic developmental corpus. The model successfully simulated the overall pattern found with children, including the absence of neighbourhood size effects. The self-organising neural network outperformed the classic interactive activation model in which frequency effects are simulated in a static way. These results highlight the potentially important role of unsupervised learning for the development of orthographic word forms.