WARREN — Robin Gibson of Portland has made the long drive north to visit her brother at Maine State Prison many times over the decades he has been incarcerated there.

But she has never traveled for such a happy reason as she did on Monday, when Gibson and other family members went to see her brother Robert “Paco” Payzant graduate with an associate of arts degree in liberal studies from the University of Maine at Augusta.

“With honors,” Gibson specified. “We are so proud of him.”

Payzant, 46, of Freeport, is serving an 18-year sentence for robbery and aggravated assault. He previously has served a 20-year sentence for armed robbery. But he and his family believe that his chance to pursue higher education while in prison — paid for through Doris Buffett’s nonprofit Sunshine Lady Foundation — has changed him for the better.

“He seems to have settled in and found his niche. This time, he’ll be prepared to go back to society,” Gibson said. “We are very, very hopeful.”

Her tall, burly brother was one of 13 inmates who flipped their “Class of 2013” tassels Monday afternoon before a prison room full of cheering, crying relatives, friends and college instructors. To a man, they gave heartfelt thanks to the 85-year-old Buffett, the sister of billionaire Warren Buffett, who sat in the first row and wore a bright yellow jacket to cheer on her new graduates.

“It’s a form of caring about people and seeing that they have a chance,” she said of her charitable work with prisoners. “We’re turning out a lot of good citizens, from coast to coast. The joys involved in this are overwhelming.”

Through her foundation, Buffett has given a total of $100 million nationally to philanthropic efforts that include providing higher education to prisoners. In Maine, she has donated nearly $1 million to that goal. Since 2006, 35 incarcerated men have earned their degrees through the University of Maine at Augusta, and so far, none of the men released after their graduations have returned to prison.

“Programs like this are what’s going to keep these guys from coming back,” Maine State Prison Warden Rodney Bouffard said after graduation was over, adding that the general recidivism rate in Maine is 70 percent. “I know society will disagree with what I’m saying … but people don’t get better because you punish them.”

The instructors and professors who worked with the incarcerated students said that the inmates worked hard for their degrees, all of which were earned in the multidisciplinary liberal studies field. Five men earned bachelor’s degrees and eight earned their associate’s degrees. All but one graduated with honors, a rate much higher than other graduating classes, a faculty member pointed out. The prisoners’ degrees do not reduce the time they have to serve.

“They’re doing this for the love of learning,” said Brenda McAleer, dean of the college of professional studies.

Chris Legore, who teaches math, said she enjoys working with the students so much that it can be hard to leave the building when class is done.

“It’s a very wonderful experience. They’re good students. They’re very driven. They know when they get out, they need to have a career,” she said. “They always have their homework done on time.”

Payzant, who wore his graduation cap and gown over his prison uniform of blue jeans and sneakers, said he isn’t the same man he was when he entered prison, or when he got out after serving his first long sentence. When he gets out in a few years, he’s interested in maybe joining the Peace Corps or continuing the hospice work he has begun while in prison.

“My world view is totally different,” he said. “I feel awesome. Having the opportunity to be in front of Doris Buffett, giving her my love and thanks, it means everything.”