This study explores the ways that state high school testing policies shape college opportunity among students attending 15 high schools in five states. The authors use multiple descriptive case studies to explore how testing policies influence key predictors of college enrollment (e.g., high school graduation, academic preparation, knowledge, and information) and a high school's capacity to promote college enrollment. The study identifies several unintended consequences of state-mandated high school tests for factors related to college enrollment and shows that the unintended negative consequences are greater at schools with the lowest average socioeconomic status and academic achievement than at other schools. (Contains 2 tables.)