In honor of Teacher Appreciation Week, “GMA” is honoring educators, including educators like Mike Peterson, a custodian-turned-substitute at Plymouth Middle School in Plymouth, Minnesota.

Before becoming the school’s favorite teacher, Peterson was a custodian for nearly three decades. He eventually became the director of the custodian program at the school and earned a bachelor’s degree in his spare time.

“I started in the district 29 years ago, working as a night person. While I was doing nights, I was going to school,” Peterson told “Good Morning America.”

When Peterson decided to retire in 2021, he came right back to the school as a substitute teacher for math, his favorite subject.

“I wanted to be a teacher and [the school gave] me a part-time job because I keep busy,” said Peterson.

Barb Wurdeman, a social studies and science teacher, said she was glad to see Peterson again in the hallways.

“Initially, I thought he came back as a custodian when I saw him in the hall. But then, [when I realized] he had a class and he came back as a substitute teacher, I was just so impressed,” said Wurdeman.

According to the Bureau of Labor Statistics, close to 600,000 substitute teachers cover over 30 million teacher absences in K-12 schools and 20% of requests for substitutes go unfilled.

Paula Engel, a Spanish teacher, said Peterson became a hero.

“When we were coming out of the pandemic, we needed substitute teachers. We were desperate. I mean, it was a big problem. And Mike solved that problem,” said Engel.

Other colleagues said Peterson inspired them.

“He was one of the reasons why I decided to go back to school and finish up getting my degree,” said John Davis, a special education teaching assistant. “It just made me think about, 'You know what? If Mr. Peterson can go back to school and do what he did to get his degrees, why can't I do it?'”

After decades of working in the district, Peterson was able to transition into the substitute teacher role seamlessly.

“You can't replace that knowledge from all those years. How can you replace somebody who knows things from 29 years of working there now?” said wife Sheri Peterson. “That's his family.”

Freedom Trotter, a school climate and culture specialist at the school, said Peterson has always been a teacher -- long before his new role.

“I would say he was a teacher before he actually became a licensed teacher. And so, it started with building those relationships with students and it carried on into the classroom,” said Trotter.

Most importantly, the students are happy to have Peterson back in the school and say he is always in a good mood and treats students like family.

“He connects more with the kids. He's more willing to talk to us and not just like sit there and be like, ‘Oh, I have to babysit these kids.’ No, he's interacting with us and making us laugh and we're just all having a good time,” said Virginia Smit, a student.

Peterson said he sees it as just being there for the people who are always there for him.

“Why not help your friends?” he said. “You know, it’s my family.”

Students, teachers, friends and family gathered Monday morning to surprise Peterson in person.

"GMA" surprised Peterson with a donation in his name through The Minneapolis Foundation to the Seven Dreams Foundation to bring teachers from diverse backgrounds and experiences into classrooms.

After the check surprise, Peterson shared an encouraging message. "You can succeed. Never stop. Go into it. I'm here for you to help you succeed and all the teachers that I've worked with, they're there for you," he said.

"That's what I'd like to introduce for the kids that are having some issues. When I was a kid I had some issues but I've learned to go and did I stumble? Yes. But I kept going and going and going and tell you the truth, through that, I've been successful. I think I have the best building. I enjoy working. It's one of those things, coming in here, it is an adventure every day in the classroom," Peterson added.

"GMA" also teamed up with Ace Hardware to surprise Peterson with a new toolset to support Peterson's side projects both at school and at home.

"I feel that all this is helping not only the kids that I love working with and for teachers and they'd be going so that people that want to sub, come on in. You know, the water is sometimes warm, sometimes cold but it's a new adventure and I think everybody needs a new adventure," Peterson said.

"And these kids need help. And I love if they can't figure out stuff that I can sit down and help them. If I can play help just one or like I wrote in my Facebook, it's like Batman going into the Flash. Save one, then save another. So if I can sit down and work with them, that's what I'm here for."