A study of charter schools in Indiana found that the test scores of students who transferred from public schools to charter schools lagged and later rebounded. But it also found very high attrition as students left charter schools and returned to public schools.

A recently released study raises questions about whether charter schools improve academic achievement for students in Indiana more than traditional public schools.

Researchers from the Indiana University School of Education-Indianapolis examined four years of English and math ISTEP scores for 1,609 Indiana elementary and middle school students who were in a traditional public school in 2011 and transferred to a charter school in 2012. The main findings were that students who transferred had lower math and English score gains during the first year or two in their new school than if they had stayed in a district school.

The researchers were able to draw the conclusion by using a type of statistical analysis that enabled them to compare students’ actual score gains at the charter school to potential gains had they not transferred from a traditional school.

But for the students who stayed in charter schools for three years or more, some of those gaps disappeared, and students caught up with where they would have been if they hadn’t transferred. Both of these results — the dip in score gains after transferring and the increase over time — are consistent with other studies, researchers said…

The researchers also found that of the original number of students who transferred to a charter school in 2012, 47 percent returned to a traditional public school by 2016. Only about a third of students remained enrolled in charter schools long enough to see their scores catch back up. The study called the mobility “problematic,” and suggested other researchers look into it further.

Well, that’s curious. Only about a third of students remained enrolled in charter schools long enough to see their scores catch back up to what they would have been if they had stayed enrolled in a public school.