This study examined the prevalence of teacher tracking in a population of 1,822 mathematics teachers in 184 high schools in a single state. Results showed that 70% of teachers were tracked by course level, course track, or both. Three fourths of high schools tracked at least 58% of their mathematics teachers. We also found significant differences in teaching assignments across quintiles of years of experience at a teacher's current school. First-quintile teachers were the most likely to be assigned low-track or entry-level courses. In contrast, fifth-quintile teachers were the most likely to be assigned high-track or upper-level courses. These findings indicate that the tracking of mathematics teachers is a prevalent and persistent inequitable structure in most high schools.