Researchers use data from the RAND American Mathematics Educator Study surveys of public school principals and teachers to investigate three school structures--referred to as "school opportunity structures" throughout this report--that may affect kindergarten through 8th grade (K-8) students' mathematics learning. These structures are tracking (i.e., grouping students by achievement level), teacher qualifications and assignments, and supports for struggling students. This report is among the first to explore school structures that support students' mathematics learning across the United States and in the four largest states: California, Florida, New York, and Texas. The authors do not examine the quality of mathematics instruction students receive or how much students have learned. Instead, they consider the ways that elementary and middle schools are organized to provide mathematics learning opportunities. Policy recommendations are aimed at helping leaders at the state, district, and school levels reflect on how schools support math learning and how school structures might be improved to set up all students for success in high school and beyond.