Although psychological theories assign to mistakes a fundamental role in the learning process and suggest ways to deal with them, only few studies have analyzed ways teacher-student interactions surrounding mistakes occur in actual classroom settings. This study focuses on such analysis. Also examined here are cultural factors that inform teacher mistake-handling. The data include a sample of 30 Italian and 30 US videotaped eighth-grade mathematics lessons. The methodology combines a discourse analytic approach with quantification of some aspects of the interactions observed. The differences observed in Italian and US lessons are interpreted as a complex interplay of two elements: beliefs about learning and culturally specific instructional practices.