School systems around the world use achievement tests to assign students to schools, classes, and instructional resources, including remediation. Using a regression discontinuity design, we study a Florida policy that places middle school students who score below a proficiency cutoff into remedial classes. Students scoring below the cutoff receive more educational resources, but they are also placed in classes that are more segregated by race, socio-economic status, and prior achievement. Increased tracking occurs not only in the remedial subject, but also in other core subjects. These tracking effects are significantly larger and more likely to persist beyond the year of remediation for Black students.