Students in K-8 schools do better than students who move from elementary to a stand-alone middle school, according to a Columbia University study published in Education Next. The study followed New York City students from third through eighth grade.

In the year students moved to middle school — sixth or seventh grade — math and English scores fell substantially compared to K-8 counterparts. Their achievement continued to decline through eighth grade.

The gap isn’t explained by spending or by class size, researchers Jonah Rockoff and Benjamin Lockwood write. Cohort size — the number of students in the same grade — was a factor. The K-8 schools averaged 75 students in the same grade; the middle schools averaged more than 200.

Developmental psychologists have shown that adolescent children commonly exhibit traits such as negativity, low self-esteem, and an inability to judge the risks and consequences of their actions, which may make them especially difficult to educate in large groups. The combining of multiple elementary schools and their students also disrupts a student’s immediate peer group. And middle schools often serve a more diverse student population than many students encountered in elementary school.

Rockoff and Lockwood aren’t sure why the transition to a larger middle school is so difficult. But they believe New York City children aren’t much different from students elsewhere.

After interviewing the study’s lead author, Columbia Business School professor Jonah Rockoff,  Martin West observes that Americans rate their local middle schools far lower than elementaries in the EdNext-PEPG Survey. “Rockoff and Lockwood’s research suggests that parents are onto something – and that the emerging trend toward shuttering middle schools and replacing them with K-8s is an encouraging development.”