Rob Gronkowski, Geneo Grissom and AJ Derby managed to squeeze an offseason workout in on April 1, but not the kind you think. 

The three Patriots worked up a sweat volunteering for the fourth annual Five Town School Day Special Olympics in Ashland, Mass., leading stations like "The Gridiron Gronk" obstacle course, "The Edelman Catch" and "The Brady Toss." 

Special Olympians from Ashland, Holliston, Medfield, Medway and Millis put their training to the test and made the Patriots work to keep up. 

"Some of the kids had some really good arms," AJ said. "I told some that Tom [Brady] needs to watch out for them coming up in the future. They had some good throws and a lot of fun today."

The day started with a parade through the school with the Olympians, the volunteers, A.J. and Geneo. Gronk made his entrance to lead the athletes in stretching before the games begin, alongside his teammates, cheerleaders and Pat Patriot.

After the opening ceremony, the games kicked off. Gronk's appearance was a surprise for the participants, and the students, volunteers and spectators were all smiles when they saw their loveable Patriot. 

Gronk ran through the obstacle course with the athletes, high fiving, dodging defensemen and diving into the end zone. Some took a page out of the tight end's own playbook and spiked the ball after completing the course. 

"A lot of Gronk spikes," Gronk said with a smile. "We saw a couple of the kids, and I gave one too. I almost hit the ceiling."

The energy in the gym at Ashland High School was contagious as spectators, family, friends and students cheered the athletes and volunteers through the stations. Students from the districts' Best Buddies clubs, football teams, National Honors Society and more helped run the event.

Though some of the school staff joked it was an April Fools Prank when they found out Gronk would be joining the fun, principal Kelley St. Coeur said the Special Olympics event was only enhanced by the Patriots presence.

"This is literally my favorite day of the year as high school principal," she said. "I'm thrilled to have the Patriots here. It means so much that they support these athletes who, for some of them, doing these small moves is so difficult for them and they're having the time of their lives. I love it."

Gronk said while giving back to the community is a priority, being able to run around with the athletes made the day at the Special Olympics stand out. 

"I definitely got a lot out of it. I'm sure all of the volunteers did too. You saw all the smiles on their faces, but what was very cool about this event was that it was interactive … I mean, to me it's important because it's just great to give back," Gronk said. "They come to support us on Sundays. They're watching us on TV and going to the games. Being able to make an impact on the community, seeing the kids run through [the obstacle course] and then have a super big smile after they tackle the little dummy guy and the kids coming to give me a high five. I mean, that's a pleasure right there, and it's super cool to see that."

For more pictures from the Special Olympics event, check out the gallery below.