The study says 48% of Promise-eligible students complete a post-secondary program within six years after high school.
That's a 12% increase compared to pre-Promise students.
Additionally, Promise students are more likely to attend a four-year college and choose an in-state school.
The increases weren't limited to students who are already advantaged.
The study found that college completion rates were just as great, if not greater, for low-income and minority students as they were for more advantaged students.
Study co-author Tim Bartik says that's an important finding, considering the universal nature of Promise.
"Money does matter," he said, "We should be looking at ways to make college more affordable for a broad range of Americans."
To qualify for the Promise, a student must attend a Kalamazoo Public School continuously from 9th grade to graduation and reside within the KPS district.
Bartik said the program's simple eligibility requirements have helped make it successful.
"[Scholarships] work much better if you make [students] an offer they can understand," he said, "The Kalamazoo Promise says, 'College is going to be free; it's up to you to take advantage of this offer.'"
The anonymously funded Promise scholarship has given more than $60 million to over 3,800 students since it began in 2005.