Tracking has been criticized for impeding the academic progress of low performing students; however, eliminating tracking has also been shown to have negative consequences, particularly for high achieving students. This study examines the consequences of a policy which sorted ninth-grade algebra classes by students’ abilities, but provided doubled instructional time and additional supports for low ability students and their teachers. Results show that low-ability students received more demanding instruction and better pedagogy; these benefits helped mitigate negative effects of concentrating students with behavioral problems together. High ability students received more demanding instruction and had fewer classmates with behavioral problems, and this led to improvements in their test scores, but higher failure rates. We discuss implications for tracking practices.