A great deal of attention has been given to the learning loss that can take place under brand new teachers, but there is a growing body of research that shows moving teachers between grade levels, or "grade switching," can actually be harmful to student achievement, too. While grade switching is a common practice for many reasons (about a quarter of all teachers in a school have switched grades any given year), there are a few things to consider when determining teacher assignments for the coming year. This document discusses the following topics for consideration: (1) Grade switching is not good for teachers; (2) The negative impact on student learning is big and can still be measured two years out; (3) "Strategic" grade switching may actually backfire; (4) The most vulnerable students are more likely to be assigned to a teacher who switched grades; (5) Teachers who switch schools see an even bigger decline in effectiveness; and (6) Keeping teachers in the same grade also helps retain teachers. Recommendations for school leaders are included.