This paper evaluates whether Washington, D.C.’s Equitable Access (EA) policy expanded access to high-demand schools for economically disadvantaged (“at-risk”) applicants by prioritizing them within the city’s unified school-choice lottery. I examine how the policy changed match rates for at-risk students at targeted schools, the extent of crowd-out among other applicants, and the stability of preferences before and after the reform. I also assess efficiency by measuring changes in applicant welfare and subsequent enrollment and persistence in the public-school system. Using administrative records from 2018–2024, I exactly replicate D.C.’s deferred-acceptance assignment algorithm and conduct policy simulations to decompose total changes in access into rule, demand, and capacity components. EA substantially increased access for at-risk applicants at participating charter schools, while the rules at traditional public schools were often non-binding. Preferences remained stable across years, indicating that the mechanical rule effect was the dominant channel of the policy. Crowd-out of non-at-risk applicants was generally limited, although significant at a few schools, and welfare gains for at-risk students occurred without measurable losses for others. At-risk applicants who received EA matches were also more likely to enroll and persist in the D.C. public-school system. In sum, these results suggest that equity goals can be implemented within assignment mechanisms not only with minimal disruption but can also yield modest efficiency gains.