Much research has described how academic achievement can suffer when a student changes schools mid-year, but new research in the journal Educational Evaluation and Policy Analysis finds that the arrival of new students in the middle of the school year also hampers the academic performance of their classmates.

Researchers Emilyn Ruble Whitesell of Mathematica Policy Research, Leanna Stiefel of New York University and Amy Ellen Schwartz of both New York and Syracuse universities studied the records of 250,000 4th- through 8th-graders attending New York City public schools between 2005 and 2008. Approximately 11,000 of these students changed schools midyear, three-quarters coming from other New York City public schools and the rest from other U.S. school districts or foreign countries. 

On average, three to four students enter a school midyear per grade, approximately one new student per class assuming 100 students per grade, according to Department of Education data. The influx of new students midyear is much greater in about 130 city schools, where the number of new arrivals is as high as eight or nine students for every 100 students per grade, or about two new student per class.

Exposure to incoming students from another New York City public school reduced the academic achievement of a school’s stable students by 2 percent of a full school year of learning.The negative impact was slightly larger when the new students came from another country or school district. Classmates who were not eligible for free or reduced-price lunch were also slightly more affected when new students arrived mid-year. In math, these negative effects persisted for several years following exposure to the transient students.

The researchers recommend school districts try to reduce exposure to high numbers of transient students by distributing students who enter mid-year more evenly across all schools.