This study examines the effects of the summer period on value-added assessment (VAA) of teacher and school performance at the early grades. The results indicate that 40-62% of the variance in VAA estimates originates from the summer, depending on the outcome. Furthermore, when summer is omitted from the VAA model, 51-61% of the teachers and 58-61% of the schools change performance quintiles. Extensive statistical controls for student background and classroom and school context reduce these differences, but 36-47% of the teachers and 42-49% of the schools are still in different quintiles. Besides misclassifying teachers and schools, including summer created biases in VAA estimates against schools with concentrated poverty. The results suggest that addressing these issues will require biannual achievement assessments.