This report examines the effects of increasing science course-taking requirements in the Chicago Public Schools. CPS has been at the forefront of the national movement to require a college-preparatory curriculum for all high school students. In 1997, CPS mandated that all entering ninth-graders take a college-preparatory curriculum in high school, including three years of science coursework. This policy change occurred several years before many states raised their science requirements and eight years before the State of Illinois instituted a more modest increase (from one to two years). The previous CPS coursework policy required just one science credit; the new policy required students to take a minimum of the following courses: earth science or environmental science, biology or life science, and chemistry or physics. To examine the impact of this curriculum policy change, this report compares outcomes for cohorts of students in Chicago before and after the 1997 policy was enacted. While the new requirements did lead to increased science course completion, the authors found little evidence of additional science learning or improved college outcomes. Three appendices are included: (1) Research Methodology; (2) Supplementary Tables; and (3) Survey Measures on Instruction. (Contains 8 tables, 14 figures and 54 endnotes.) [This report was written with Macarena Correa.]