School districts across the United States increasingly use value-added models (VAMs) to evaluate teachers. In practice, VAMs typically rely on lagged test scores from the previous academic year, which necessarily conflate summer with school-year learning and potentially bias estimates of teacher effectiveness. We investigate the practical implications of this problem by comparing estimates from “cross-year” VAMs with those from arguably more valid “within-year” VAMs using fall and spring test scores from the nationally representative Early Childhood Longitudinal Study–Kindergarten Cohort (ECLS-K). “Cross-year” and “within-year” VAMs frequently yield significant differences that remain even after conditioning on participation in summer activities.

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Teacher churning likely harms student achievement. However, the phenomenon of within-school grade-level teacher reassignments is understudied. The current study provides descriptive evidence on the frequency and predictors of within-school teacher grade switching using both longitudinal administrative data from Michigan and nationally representative survey data. About 7% of self-contained classroom teachers change grades following any given school year. Inexperienced teachers are relatively more likely to switch grades, and grade-level reassignments are inequitably distributed across both schools and students. For example, urban schools experience significantly higher rates of grade switching. Charter schools experience significantly less grade switching than traditional public schools.Keywords teacher retention, teaching assignments, school quality, teacher turnover Teacher turnover, whether measured by attrition from the profession or mobility across schools, can disrupt the functioning of schools in a myriad of ways. For example, high rates of teacher turnover may reduce instructional

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