There is mixed evidence regarding the effects of multigrade classrooms on student achievement. Because the constrained fiscal environments facing many of the nation's districts may lend fresh impetus to this practice, it is important to understand how students placed in these classrooms perform relative to their peers. This paper presents new evidence from the Los Angeles Unified School District schools on the achievement of students in multigrade classrooms and uses a quasi-experimental method to define a plausible comparison group of peers in a monograde classroom. It seeks to examine how these students would have performed had they been in a monograde classroom. The authors found that being in a multigrade classroom had consistently small and negative effects on student achievement, regardless of grade or subject, even controlling for teacher characteristics. However, none was large enough to be substantively significant. The benefits of multigrade classroom, if they exist, are unlikely to accrue unless teachers are trained and adequately supported when placed in such classrooms.