Students who attended a KIPP middle school a decade ago were 13 percentage points more likely to enroll in college as a result, according to a new study of the country’s largest nonprofit charter school network.

KIPP cheered the results. “We made a commitment 25 years ago to help students climb the mountain to and through college, and these numbers show that we are moving closer to delivering on that promise on a national scale,” CEO Richard Barth said in a statement.

But the study can’t definitively say whether the charter network had an effect on students actually staying in college, and not enough time has passed to draw conclusions about college completion.

It’s the first rigorous attempt to measure the longer-term effects of KIPP, which pioneered an influential, much-debated “no-excuses” approach to running schools largely for low-income black and Hispanic students. KIPP, which just celebrated its 25th anniversary, now has 242 charter schools across the country in its network and recently won a large federal grant to continue growing.

The latest study builds on a 2013 paper that looked at about 1,000 students who applied to a KIPP middle school in 2008 or 2009. The initial research found that students who won the lottery had substantially higher math scores two years later compared to students who lost the lottery. (Other studies of KIPP have also shown that its schools produce large test score gains.)

The researchers continued to follow those students for this latest study. Attending KIPP, they found, had a large effect on four-year college enrollment: 52% of KIPP students enrolled in a four-year college within two years of completing high school, compared to 39% of those who didn’t go to KIPP.

That’s a big boost, comparable to the national gap in college enrollment between white students on the one hand and black and Hispanic students on the other.