Recent studies have revealed how large shares of college-ready students undermatch, or enroll in colleges with less competitive admissions processes than they are eligible to attend. Undermatch sits at the nexus of both college access and completion agendas, as undermatching to a less selective institution results in a decreased likelihood of graduating from college. Latino, low-income, and potential first generation college graduates are more likely to undermatch than their nonunderrepresented peers. Many underrepresented students rely on their high schools to help navigate the college choice process, yet we have a limited understanding of how high school characteristics can inhibit or promote the likelihood of undermatch. This study used ELS:2002 data to model within the HGLM framework the likelihood of undermatch. In order to explain the observed variations in undermatch at the high school-level, I measured high school-level predictors in two distinct ways: confirmatory factor analysis to identify individual high school-level measures of college-promoting resources and norms; as well as latent class analysis to create a typology of high school contexts. Findings suggest that students who attend high schools with above average, rather than average, college-promoting resources and norms are less likely to undermatch at the time of application and enrollment, after controlling for student-, school-, and state-level characteristics. Net of other variables, students who were not high income and whose parents did not have a bachelor's degree were more likely to undermatch than their peers. Smaller shares of Black, Latino, low-income, and first-generation students were eligible to attend selective institutions, larger shares undermatched by qualification level, and larger shares were in low-resourced high schools. Policy implications and directions for future research are discussed.