Many students find math difficult, but those who are intrinsically motivated learn and do well even when they face obstacles. Here, the authors examine an environmental factor that might affect students' intrinsic motivation in math: namely, teachers' beliefs about success in math. Do teachers perceive elementary school math as a domain that requires an innate ability, and does this belief relate to students' intrinsic motivation in math? Our study explored these questions in a sample of 830 German fourth graders and their 56 teachers. Teachers reported stronger beliefs in the role of innate ability for math than for German language arts. In addition, the more teachers believed that math requires innate ability, the lower was the intrinsic motivation of their low-achieving students. These results suggest that teachers’ beliefs that math success depends on innate ability may be an important obstacle to creating a classroom atmosphere that fosters engagement and learning for all students.