Background: This longitudinal study examines the long-term effects on the achievement of students at a diverse suburban high school after all students were given accelerated mathematics in a detracked middle school as well as ninth-grade "high-track" curriculum in all subjects in heterogeneously grouped classes. Despite considerable research indicating the ineffectiveness and inequities of ability grouping, the practice is still found in most American high schools. Research indicates that high-track classes bring students an academic benefit while low-track classes are associated with lower subsequent achievement. Corresponding research demonstrates that tracks stratify students by race and class, with African American, Latino and students from low-socioeconomic households being dramatically over-represented in low-track classes and under-represented in high-track classes. Purpose: In light of increasing pressure to hold all students to high learning standards, educators and researchers are examining policy decisions, such as tracking, in order to determine their relationship to student achievement. Design: This study used a quasi-experimental cohort design to compare pre- and post-reform success in the earning of the New York State Regents diploma and the diploma of the International Baccalaureate. Data Analysis: Using binary logistic regression analysis, the authors found that there was a statistically significant post-reform increase in the probability of students earning these standards-based diplomas. Being a member of a detracked cohort was associated with an increase of roughly 70% in the odds of IB diploma attainment and a much greater increase in the odds of Regents diploma attainment--ranging from a three-fold increase for White or Asian students, to a five-fold increase for African American or Latino students who were eligible to receive free or reduced-price lunch, to a 26-fold increase for African American or Latino students not eligible for free or reduced-price lunch. Further, even as the enrollment in International Baccalaureate classes increased, average scores remained high. Conclusion: The authors conclude that if a detracking reform includes high expectations for all students, sufficient resources and a commitment to the belief that students can achieve when they have access to enriched curriculum, it can be an effective strategy to help students reach high learning standards.