New research suggests that teaching a new grade is challenging and reduces a teacher’s effectiveness in the short term for most teachers.

Teachers who are assigned to teach in a different grade than the one they taught during the previous school year have smaller value-added scores than teachers who repeatedly teach the same grade year after year, according to new research from Education Researcher. The impact of switching grades on teacher value-added scores can wipe out the annual gain a teacher realizes from having an additional year of experience.

David Blazar, a researcher from the Harvard Graduate School of Education, studied 10 years of human resource information on 20,000 elementary school teachers working for an urban school district in California who had two or more years of experience. He found that switching grades was a common occurrence, affecting about 17 to 20 percent of elementary school teachers each school year.

The rate of switching was highest for newer teachers: Almost 24 percent of teachers with four years of experience switched grades in a given year versus only 11 percent of teachers with nine or more years on the job.

Blazar found teachers’ value-added scores declined by 20 to 30 percent from the year prior to the year of the switch, with the largest declines occurring for math teachers. Switching to a nonadjacent grade resulted in the largest decline in value-added scores and these lower scores persisted for several years following the switch.

When teachers with five or more years of experience switched to an adjacent grade, they actually saw their value-added scores rise in both ELA and math for the year following the switch.

Blazar suggests that school leaders should create opportunities for teachers, particularly those in the early years when they are still learning the craft, to have the same grade assignments.