Twiictée, a portmanteau of Twitter and dictée (French for dictation), is a collaborative method for teaching spelling that promotes the metacognitive reasoning needed to understand and assimilate the morphosyntactic features of French spelling. The present study evaluated Twictée’s impact on spelling performance in 40 classes of 4th-, 5th-, and 6th-grade students (N = 893 students). Mixed-model analyses showed a significant improvement in global spelling performance over time, but the impacts of the interaction between time and condition reached significance for only four specific aspects of spelling performance. Nevertheless, further analyses showed that Twictée’s overall impact on spelling performance was significantly greater in schools in disadvantaged urban areas and in large classes. We discuss these results in the light of previous qualitative analyses carried out on this corpus.