The opportunity to take college courses in high school (dual enrollment) is becoming increasingly prevalent, but access is not equitably distributed. Certain populations, such as economically disadvantaged students and students who are members of racial and ethnic groups historically underrepresented in college, are less likely to take dual enrollment courses. This paper presents findings from an evaluation of the College and Career Readiness Expansion Project, an effort to expand participation in dual enrollment courses within the context of broader changes in high schools. A quasi-experimental impact study showed that the project successfully expanded access, particularly for economically disadvantaged students. Implementation data showed that the schools participating in the project used a variety of strategies to expand access, including: (1) understanding and using data; (2) increasing students' awareness of college courses and their importance; (3) supporting students' college readiness; (4) removing eligibility barriers; and (5) providing support for students taking college classes.