In 1997, Chicago implemented a policy that required algebra for all ninth-grade students, eliminating all remedial coursework. This policy increased opportunities to take algebra for low-skill students who had previously enrolled in remedial math. However, little is known about how schools respond to the policy in terms of organizing math classrooms to accommodate curricular changes. The policy unintentionally affected high-skill students who were not targeted by the policy--those who would enroll in algebra in its absence. Using an interrupted time-series design combined with within-cohort comparisons, this study shows that schools created more mixed-ability classrooms when eliminating remedial math classes, and peer skill levels declined for high-skill students. Consequently, their test scores also declined. (Contains 15 notes, 6 figures, and 5 tables.)