Taking advanced courses in high school predicts a broad array of positive postsecondary and labor market outcomes. Yet students from historically disadvantaged groups and low-income backgrounds have long been underrepresented in these courses. To address this problem, more than 60 districts in Washington state implemented a policy that automatically enrolled all qualified high school students in advanced coursework. The policy relied on a simple behavioral nudge: It made advanced courses “opt out” rather than “opt in” for all qualified students. The districts implemented the policy in waves, beginning in the 2014–15 school year. In this descriptive paper, we examine enrollment patterns by comparing districts that adopted the policy at different times. We found that students in districts that implemented the policy between 2014–15 and 2016–17 were more likely to enroll in at least one advanced course in any subject relative to students in districts without the policy. This was the case for students who “qualified” for advanced courses based on their test scores and for students whose scores did not qualify them for advanced courses. We also found that the policy was associated with a higher probability of enrollment in advanced mathematics courses but only for qualified students. Qualified students across demographic groups experienced similar changes in the probability of advanced course enrollments. But among all students—regardless of qualified status—enrollments in advanced mathematics and advanced English language arts/social studies courses increased more for students from racial/ethnic groups underrepresented in advanced courses and for students who were eligible for free or reduced-price lunch (FRPL) than for non-underrepresented students and students not eligible for FRPL. These across the board increases in advanced course enrollment for students who were historically underrepresented in these courses suggests that districts may have looked beyond standardized assessment scores to identify students for automatic enrollment.