One explanation for negative or null findings in prior research on postsecondary remediation is that college may be too late to address issues of academic underpreparedness. This study evaluates the impact on student outcomes when college math remediation is offered in the senior year of high school. The Seamless Alignment and Integrated Learning Support (SAILS) program in Tennessee targets students with low eleventh-grade ACT math scores. Students who pass SAILS in twelfth grade can enroll directly in college-level math courses at any Tennessee community college. Using a triple-difference design, we exploit variation in students' treatment status based on ACT math scores (remediation-eligible versus remediation-ineligible), high school adoption of SAILS (first cohort versus later cohort), and senior year (before versus during first SAILS year). We find that SAILS-eligible students in the first cohort were significantly less likely to enroll in remedial math courses in college, and more likely to enroll in and pass college-level math overall. These students also earn 2.8 additional credits by their second year. We detect no significant differences in high school graduation rates, college enrollment, or postsecondary credential attainment within two years. The program advanced progress toward several, but not all, of the potential goals examined.