The "High Schools That Work" school improvement initiative is the nation's largest comprehensive school reform model with over a thousand schools adopting its framework. The initiative's premise is that all students can meet the demands of a college preparatory curriculum if provided the right supports. Analyzing over a decade of data on student course taking and performance, we employ a rigorous comparative interrupted time series strategy to assess the extent to which "HSTW" meets its goal by increasing students' successful progression through the mathematics and science pipelines. Each pipeline consists of three college preparatory courses: algebra 1, geometry, and algebra 2 in mathematics and biology plus two physical science courses in science. The results show no effect on pipeline progression for the average student and some evidence of increased gaps in course taking between more advantaged and disadvantaged students. (Contains 2 figures, 11 tables, and 4 exhibits.)