Whereas subject-area specialization is common practice in secondary grades, little is known about its incidence and impact in elementary schools. In this study we use data from North Carolina elementary schools to assess which teachers specialize and estimate whether specialization is associated with teacher effectiveness and school achievement. We find that specialization is prevalent in upper-elementary grades—approximately 25 percent of fourth-grade teachers and 37 percent of fifth-grade teachers specialize—and schools assign relatively more effective teachers to specialize. Analyses indicate that specialization is not leading to its theorized benefits in mathematics and reading. Teachers are less effective than they were before specializing and school-level achievement is not associated with more specialization. However, science results suggest benefits to subject-area specialization. These findings question the use of specialization in elementary grades but invite continued research to more fully assess its impact.