School choice policies necessarily impose registration timelines, constraining access to schools of choice for students who register late. Drawing on administrative data, survey data, and interviews with 33 parents in Boston, we find that late registration is common and highly stratified: Nearly half of black kindergarteners miss the first registration deadline, a rate almost three times higher than their white peers, consigning them to the least preferred schools. Contexts of instability and bureaucratic complexity serve as barriers to registering months in advance, and parents describe disengagement from the school system following their late registration. These findings show how despite equal access in theory, bureaucratic structures such as timeline-based lotteries hinder many families, particularly those disadvantaged already, from full participation. Inequality in school choice outcomes and experiences thus results not only from families' selections, the focus of previous research, but also the misalignment of district bureaucratic processes with family situations.