The National Math + Science Initiative's (NMSI's) College Readiness Program (CRP) is an established program whose goal is to promote science, technology, engineering, and mathematics education in high schools to improve students' readiness for college. It provides teacher, student, and school supports to promote high school students' success in mathematics, science, and English Advanced Placement (AP) courses, with a focus on students who are traditionally underrepresented in the targeted AP courses. Through a federal Investing in Innovation Fund (i3) validation grant awarded to NMSI in 2011, CRP was implemented in a total of 58 high schools in two states--Colorado and Indiana--beginning in the 2012-13 school year. American Institutes for Research (AIR) conducted an independent evaluation of the impacts of CRP on students' AP outcomes in these schools for the three cohorts of schools that adopted the program in sequential years, using a comparative interrupted time series (CITS) design that matched comparison schools to program schools in the two states. Overall, schools implementing CRP demonstrated significantly larger increases in the share of students taking and passing AP tests in targeted areas relative to comparison schools in each of the three cohorts of schools, and the gains in CRP schools were sustained over time. Fidelity of program implementation was evaluated using a fidelity matrix approach required as part of the National Evaluation of the i3 program, which showed that not all elements of the program were implemented with high fidelity. Teachers and students were not always able to attend all meetings, and schools did not always meet negotiated enrollment targets. Teacher survey data indicated that teachers found the professional development activities provided by CRP to be the most helpful support they received under CRP, and students reported that the tutoring and special study sessions were the most helpful. Although the program provided financial incentives to both teachers and students that were tied to student performance on AP tests, these incentives were considered the least important element of the program by both teachers and students