Maybe this won't surprise folks, but New York City students who moved from elementary to middle schools fared much worse academically than similar students who stayed within K-8 schools, according to a study written about in the latest Education Next.

The researchers aren't sure why, but they say per-pupil funding and class sizes are about the same in both. They speculate that part of the problem may be that middle schools combine students from multiple elementary schools, and that cohort sizes are much bigger in middle schools than K-8's.

"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 encounter in elementary school," they write. "Yet while it seems plausible that these changes in environment would matter, we could not find any evidence in our data that any one hypothesis can explain the drop in learning among students moving to middle schools."

Theories, anyone? And should there be more K-8's around here?