When New York University Professor Liang Zhang started doing research on veterans in higher education, he wasn’t surprised to see that the Post-9/11 GI Bill generated a significant bump in college enrollment.

But what he wasn’t expecting to learn as part of his new “Veterans Going to College” report is that the largest growth has been among veterans earning advanced degrees — particularly older veterans who already have a master’s.

It’s unclear why, exactly, more veterans are pursuing advanced degrees under the Post-9/11 GI Bill, because the U.S. Census Bureau data that Zhang used for his research did not ask about intent. But the professor has a theory: The Post-9/11 GI Bill is more “transparent” than its predecessor, the Montgomery GI Bill.

“Now college is all free. On top of that you get housing benefits. I think that part makes (graduate school) more attractive,” he said.

Multiple veterans who responded to a Military Times query agree. The Post-9/11 GI Bill, enacted in 2009, represents a significant expansion of education benefits. Without having to pay into the benefits, as with previous iterations, student veterans get up to 36 months of in-state tuition covered at public universities and stipends for textbooks and housing. At private universities, the GI Bill caps at a certain amount — $22,805.34 for the 2017-18 school year. Students at some schools who have entered into an agreement with the U.S. Department of Veterans Affairs can also receive help through the Yellow Ribbon Program, a supplement to the GI Bill that reduces or eliminates costs not covered by the GI Bill.

“I know for a clear fact that I probably would not have been able to go to school for graduate work without any help from the Post-9/11 GI Bill,” said Laurence Bennett, a 46-year-old Army veteran with an MBA. Bennett, who paid into the Montgomery GI Bill when he joined the military in 1997 and later switched to the Post-9/11 GI Bill, is about to start on a second master’s degree in project management at DeVry University‘s Keller Graduate School of Management.

“I feel that if I used the (Montgomery GI Bill) there would have been no way to finish a degree. With rising costs of school tuition and loans, it would have helped but possibly not enough,” he said in an email.

Zhang, who teaches at the NYU Steinhardt School of Culture, Education, and Human Development, said Monday his research showed about a 10 percent increase in overall veteran college enrollment. Among veterans with at least one master’s degree pursuing a second master’s, doctorate or other advanced degree, there has been about a 30 percent growth.

This result was somewhat surprising because veterans with master’s degrees were eight years older than the average veteran in his sample group, and older people are less likely to attend college, he writes in the report.

“From another perspective, however, because education improves one’s decision making, better educated veterans may be more likely to make informed decisions and take full advantage of the generous education benefits offered by the (Post-9/11) GI Bill,” the report said.

Zhang’s study also found that the Post-9/11 GI Bill’s effect on college enrollment was much larger immediately after the bill’s adoption and has plateaued in recent years. In addition, he found that there has been a consistent and positive impact on enrollment across all age groups studied, ranging from 20 to 60 years old.

Much like Bennett, Army veteran Maureen Elias, 40, said she would have never attempted to go to graduate school without the Post-9/11 GI Bill.

“There is no way I would have chosen to go into $60,000 or more into debt,” the former counterintelligence agent and mother of three said in an email.

Elias earned a bachelor’s degree at Campbell University in 2012 and will graduate in December with a master’s in mental health counseling from Bowie State University. After separating from the Army in 2006, Elias and her husband, also a veteran, started to seriously consider going to college once they heard about the Post-9/11 GI Bill.

“Because Campbell University is a private university and had a high tuition cost, we received more money through the tuition payment and monthly stipend with the Post-9/11 GI Bill instead of using the Montgomery GI Bill,” she said. “It also seemed like a much less complicated formula for payment because tuition was paid directly to the school. We were thrilled when we found out we also got a book stipend because we learned very quickly that college books are expensive.”

Zhang acknowledged there could be changes coming to the Post-9/11 GI Bill soon, with the passage through Congress of the “Forever GI Bill,” which will bring even more expansion to the education benefits. And while he can’t say what the effect will be at this point, as President Trump has yet to sign it into law, Zhang said there could be similar effects.

“Basically, the punch line is that the expansion matters,” he said.