ZION, Ill. -- A senior prank at a north suburban high school seemed humorous at first, but as a group of students quickly learned, the administration isn't amused by monkey business.

Images: Monkey Business Video: Students Suspended After Prank

And so -- after 10 students in larger-than-life banana costumes ran the halls of Zion-Benton Township High School with an 11th student dressed as a gorilla giving chase --- the boys are on the raw end of a seven-day suspension.

The prank started when senior Andrew Leinonen, who will study criminal justice at Carthage College this fall, wanted to do something that wouldn't damage property or hurt anyone, while still being hilarious. After brainstorming with a few buddies, they came up with the banana idea.

"What's funnier than a gorilla chasing bananas through a school? Nothing," Leinonen said. "It was a harmless prank."

Leinonen -- who played the gorilla -- went on a recruiting mission, quickly finding 10 guys willing to pay $30 each for a banana costume. The group drew up a plan and picked a route. They planned to wear black pantyhose on their heads to remain anonymous, and even planned for escape vehicles.

They entered the school's main entrance around noon last Thursday and made their way through the English and science hallways before running into a crowded lunch room and out a back door. All the while they flailed their arms and yelled "Seniors '08."

The prank was quick, but four bananas were rounded up by school security, and by the next day, the boys had been slapped with a seven-day suspension and are at risk of missing prom and being kept off the stage at graduation.

"We all had a good idea that we were going to get in trouble," said one of the Banana Boys. "We didn't think we'd get nearly as much trouble as we did."

Zion-Benton Superintendent Deborah Clarke wouldn't comment on the punishment, citing student confidentially concerns, but she did say the school followed guidelines in place for what they consider "serious pranks."

"We're basically enforcing our policy," Clarke said.

The same policy led to five-day suspensions for kids caught fighting in school.

The punishment was not welcomed at first. None of the "Banana Boys" had ever been in big trouble and most said they're good students who just wanted to do something memorable.

In support, other students planned protests. A private group dedicated to "Saving the Banana Boys" was set up on MySpace.com.

NBC5's Natalie Martinez reported that the prank did not come as a surprise to everyone. The students' parents called them out for the day, many of the teachers had heard about the prank, and a lot of the student were amused by it.

Fearing the school may carry out its threat to keep them from prom and graduation, the Banana Boys said they advised others to relax and agreed to peacefully serve their punishment before returning to class May 2.

"We think this is a just punishment," said Brendon Epker, a banana who'll attend Calvin College in Grand Rapids Mich., in the fall. "We broke rules we shouldn't have broken."

Admittedly, the idea could have been thought out better, Epker said. Pantyhose on their heads probably wasn't the best idea, and calling in sick to pull off the prank didn't make administrators too happy. The boys were told the school responded with a long suspension because they wanted to discourage others from topping the prank, Leinonen said.

Despite the recent scares of school violence, many in the community were supportive, Martinez reported.

"The kids that are not quite so good might take advantage of the situation, and maybe hide rifles or guns of some sort," said Joie Knepper. "But, (don) constumes, run through the school -- we don't know."

The aftermath hasn't been all bad though. The boys have become mini celebrities. One received free ice cream at Culver's because of his role in the prank. And Jody Walker said his grandma was proud to say her grandson was one of the Banana Boys when the subject came up at a local pre-school.

"We have a lot of people supporting us. There are a lot of people telling us this was a great prank -- it was well done," Epker said.

Additional information provided by Sun-Times News Group