Gerry is seen as kind and funny, although he can be serious sometimes. After a stewardess on the plane going to Camp Hope gives him a pilot's wings pin to wear, he is addressed as "Captain" by the other kids at Camp Hope. At first, Gerry dislikes the name, but eventually changes his mind and takes a liking to being seen as the leader. This is shown during the go-kart relay race when Josh gives Gerry his pilot wings pin. Pat and the other kids salute Gerry while Josh says, "Take him down, Captain", to which Gerry smiles and returns the salute.
Initially, Gerry disliked the idea of going to a summer weight loss camp for boys. However, Roy, one of his fellow campers, says that Gerry will not be picked on at Camp Hope because everyone is the fat kid at Camp Hope. Hearing this, Gerry changes his mind and realizes that Camp Hope is actually a lot of fun.
As school ends for the summer, Gerry is sent by his parents to Camp Hope, a weight loss camp for boys, despite his protestations, as well as telling them he has plans to hang out. Despite worrying at first, Gerry makes friends easily at the Chipmunk Cabin (which the boys have named a long time ago). He also learns that Camp Hope is actually a lot of fun (as well as not nearly as bad as he first thought), and discovers that the other campers have smuggled in enough junk food to easily stave off the hunger pangs and probably counteract any weight loss that the camp programs cause.
The first night of the summer brings the revelation that the original owners of Camp Hope, Harvey (Jerry Stiller) and Alice Bushkin (Anne Meara), have entered bankruptcy, and Tony Perkis (Ben Stiller), a fitness entrepreneur, has (seemingly) bought the camp. (It turns out that his wealthy father actually bought it for him.) Tony announces his plan to make the camp’s new exercise regimen into the top weight loss infomercial in the country. Although Tony tries to make himself seem like someone the campers can relate to, even saying that he was a fat kid when he was younger, his methods of motivating the campers border on psychotic.
Tony cleanses the cabins of the campers’ food caches, cuts off their contact with the outside world and installs an exercise outline of trendy fitness techniques that downplay fun to the point of humiliation. During this event, Josh (Shaun Weiss) taunts Tony while in the protection of Gerry, and ends up getting kicked out of the camp without a refund. Many campers question what Josh’s fate was after this event. Josh’s father, who is a lawyer, threatened to sue Tony; as a result, Tony has no choice but to allow Josh to return to the camp.
One day when Tony goes out for a run, Gerry, Josh and a few other campers sneak into Tony’s office to search for food, and find that Tony was holding onto all of the letters the campers sent to their parents that complained of their hardships. As they leave the office, Gerry and his friends come across a fellow camper eating a hamburger. The camper tells them of a secret food stash in the forest. The campers eventually gain more weight (despite Tony’s fitness regimen), which Tony notices after measuring some of the campers’ weight losses. As punishment, Tony forces them on a 20-mile hike, reasoning that this will not only help the boys work off some of their extra weight, but will also restore discipline.
On the hike, the campers trick Tony into falling into a deep pit, and then bring Tony back to camp, where they imprison him in a makeshift cell that consists of chicken wire electrified with a bug zapper. With Tony in custody, the campers openly rebel against Tony’s counselors, tying them to trees and tormenting them. The original Camp Hope staff are left free while Tony’s workers are thrown out, except for Tony’s cameraman Kenny, who did them no wrong, and a counselor named Lars (Tom Hodges). At first, Lars is teased by the campers when his tough guy mask falls away, but is eventually given a choice — recognize the authority of the children and join the new Camp Hope, or stay tied to the tree and face deportation for not working. Lars enthusiastically joins the children.
In the celebration of Tony’s downfall, there is a lot of binge eating. Gerry and the other boys, along with some of the camp counselors, order in pizzas and submarine sandwiches, and gorge themselves on chocolate and soda, while Lars hands out éclairs. The next morning, Pat Finley (Tom McGowan), a counselor who had come to Camp Hope every summer since he was 10, tells the kids to finally start taking responsibility and start actually losing weight. The boys begin following a more healthy regime, and start to make Camp Hope a fun place again.
On Parents’ Visiting Day, the parents are shown a video of Tony’s cruelty. While they are watching, Tony escapes his prison and, when the video ends, begins clapping sarcastically from his perch on the second story. He then does a flip from the second story and lands on the floor. When Gerry calls that Tony has to be stopped, Tony begins walking on broken glass and heading over to where Gerry is while saying that he cannot be stopped, and exchanges quips with Gerry’s father, who punches Tony before telling him that he is wrong and that he is through at Camp Hope. In an attempt to make an impressive exit, Tony attempts a series of back-flips before stumbling and finally incapacitating himself. The parents and their kids look down at the fallen fitness guru as their way of telling him his days of terrorizing their kids are over, while Gerry and Pat slap their hands together. When Tony’s own father, Tony Perkis Sr (also played by Ben Stiller), shows up, he takes the keys and deed for the camp away from his son to ensure this does not happen again, and also states that the camp will be closed, and all of the money paid for admission refunded.
However, Gerry and the rest of the other campers do not want to leave Camp Hope. Since there is no adult in charge of the camp now, Pat is voted to be the head counselor. Pat starts really putting the campers to work to win an annual competition against some athletic and competitive campers from an MVP camp, who are trained to go at this competition with everything they have (which, up until Pat took over, made the competition rather one-sided). Pat, however, has been training them not to lose hope, and just to have fun, which they do. It turns out that they have just enough ability to win. Pat gives the trophy to one of the kids, who then throws it into the lake after the opposing camp throws a tantrum over losing. The competitive campers believe that Pat is crazy for being more concerned about having fun than winning a trophy.
Gerry then thanks Pat for “the best damn summer of my life”, and Pat smiles. Finally, Pat and Gerry hug.