From a constructivist perspective on learning, mistakes are seen as natural elements of learning processes. A supportive and constructive way of dealing with student mistakes has shown to affect students' individual motivation and learning performances in a favorable way. In classroom settings, however, making mistakes is not just a personal but also a social event. Dealing with mistakes should therefore be considered as both studentlevel and classroom-level characteristic. This study investigates three aspects of dealing with mistakes and their relevance for students' achievement and motivation in English as a foreign language by analyzing the aspects at student and classroom level. The aspects are a) teacher attitude toward mistakes, b) teacher response to student mistakes, and c) students' perception of mistakes as useful for learning. Analyzing data of 5266 students from 427 classes in German secondary schools, the results demonstrate that at student level, all three aspects of dealing with mistakes affect students' individual achievement as well as motivation in English language class. At classroom level, none of the aspects affect student average achievement. Two aspects affect student average motivation at the classroom level, namely a) teacher attitude toward mistakes and c) students' shared perception of the usefulness of mistakes for learning. Our results show that students' individual and shared perception of dealing with mistakes affect students' motivational and cognitive learning outcomes in different ways. Furthermore, our findings underline the relevance of teachers' attitudes as well as students' perceptions concerning mistakes for student learning and motivation in English as a foreign language class.