Racialized tracking is central to sociological explanations for racially stratified educational outcomes. However, school officials' decision-making is of debated importance for explaining racialized tracking. We contribute to this literature by examining the effects of schools' enrollment policies for Advanced Placement (AP) courses. Using a unique combination of school survey data and administrative data from Wisconsin, we examine what happens to racial inequality in AP participation when school officials enforce performance-based selection criteria, which we call "course gatekeeping." We find that course gatekeeping has racially disproportionate effects. Although racialized differences in prior achievement partially explain the especially large negative effects among students of color, course gatekeeping produces Black-white and Hispanic-white disparities in participation even among students with similar, relatively low prior achievement. We further find that course gatekeeping has longer-run effects, particularly discouraging Black and Asian or Pacific Islander students from attending highly selective four-year colleges.