The current paper reports on the Teacher Education and Development Study in Mathematics (TEDS-M). The TEDS-M surveyed selected samples from four populations in teacher education systems: future primary teachers; future secondary teachers; teacher preparation institutions; and teacher educators. TEDS-M shows that it is possible to design sampling plans for teacher education that are sensitive to local conditions and meet high technical quality standards for comparative research. In conclusion, the authors recommend that teacher educators and policy makers should pay attention to the emphasis, kind, and depth of the opportunities to learn provided to future teachers.