A significant and growing English learner (EL) population attends public schools in the United States. Evidence suggests they are at a disadvantage when entering school and their achievement lags behind non-EL students. Some educators have promoted full-day kindergarten programs as especially helpful for EL students. We take advantage of the large EL population and variation in full-day kindergarten implementation in the Los Angeles Unified School District to examine the impact of full-day kindergarten on academic achievement, retention, and English language fluency using difference-in-differences models. We do not find signficant effects of full-day kindergarten on most academic outcomes and English fluency through second grade. However, we find that EL students attending full-day kindergarten were 5 percentage points less likely to be retained before second grade and there are differential effects for several outcomes by student and school characteristics. © 2011 by the Association for Public Policy Analysis and Management.