Holistic admissions practices require evaluating an applicant's credentials in light of the opportunities available in their high school context. High school grades, test scores, and course taking are clearly related to college grades, retention, and graduation. But does performance in high school context also relate to college success? Building a unique dataset of 2.3 million students in a Midwestern state, we find that contextualized indicators of high school grades and standardized tests are strongly associated with student success in college, validating their use in holistic admissions. Contextualized grades have a stronger and more consistent association with college success than contextualized test scores, and may be most helpful at test-optional, test-free, and broader-access colleges that have yet to adopt holistic admissions practices.