SIOUX FALLS, S.D. (AP) — Behind the sturdy walls and clanking cells of the prison up on the hill, Jerry Jackson sat in math class.

The 47-year-old from Wichita, Kansas, is in his third year at the South Dakota State Penitentiary in Sioux Falls, and he's got just under a decade to go before parole eligibility.

Jackson doesn't want to put that time to waste, so he spent the last few months taking classes to receive his general equivalency diploma, or GED.

He was one of about 20 inmates at the state penitentiary to be recognized for achieving that goal. Ranging in age and sentences, the men sported red and black robes and caps donated by local high schools at the graduation celebration on May 10 in the prison's visitor room

The dimly lit room was brighter for a moment.

A thin banner of congratulations was taped over a large mirror in the front of the room; chocolate sheet cake awaited the graduates in the back. A man in a tan inmate uniform greeted guests just buzzed through double security doors with a program featuring Futurama's Professor Farnsworth.

A podium was stationed next to Pepsi vending machines.

The rounded security mirrors reflected a cluster of smiles and hands proudly clutching GED certificates.

"I'm proud of myself," said Jackson, who dropped out of high school about 30 years ago. "This is something to change my life. I was running with the wrong crowd, drugs, drinking. I used to play football, run track. I disappointed my parents."

Codington County native Joseph Carpenter had a similar story.

Now 30 years old, he dropped out of high school after getting involved with the wrong people. He turned to drugs.

"That's why I'm in here," he said.

Carpenter at first wasn't too interested in the GED program. His time in a Florida prison made the idea a bit sour to him. His brother convinced him it was something he needed to do.

"Just getting it is something I never thought I could do," Carpenter said. "It gave me tools for the outside world."

That's why staff pushes the program, warden Darin Young said.

"If you have opportunities to improve, your self-worth goes up, and you want to do more," Young said. "Receiving a GED is not easy. Receiving one in prison is not any easier."

About 120 Department of Corrections inmates have received their GEDs statewide so far this fiscal year, the Argus Leader reported. About 170 received their certificate last year, and 140 or so the year before.

"It improves the quality of life here," Young said. "You have a more positive outlook. When they leave to go get jobs, it'll give them a running start."

The work was tough.

Jackson hadn't seen a classroom in about 30 years. The first time he typed anything was while he was in prison. Having quit the program once, he was never really confident he was going to pass the final test.

A teacher made the difference. "The teachers here are really helpful," Jackson said. "They told me I could do it and I did it."

GED instructor Dave Baumeister was a big influence for Jackson.

"Jerry (Jackson) worked really hard," Baumeister said. "He passed one test after another. He never gave up."

To be eligible for parole, an inmate has to be enrolled in the GED program. Some may participate just for that eligibility, but Baumeister said most of the students genuinely want to succeed in the class.

Jackson hopes to use his new education to get a job making braille books, maps and graphs. He's been in the braille program since January and would like to continue that work when his sentence is up.

"When I get out of here and get a job, I can say I got a diploma," Jackson said. "I accomplished something."

Carpenter's graduation fell a few days before his first day of parole. He had a look of hope clutching his certificate, talking about his children and his aspirations to go to college.

He's ready to put the life that got him in prison behind him. He wanted one thing to be clear to those outside of the walls:

"Stay away from (methamphetamine)," he cautioned. "If you start it, you're going to end up dead or in prison."

He's looking forward to enrolling in community college. He wants to study criminal justice.

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Information from: Argus Leader, http://www.argusleader.com