"Pre-School" is the tenth episode of Season Eight, and the 121st overall episode of South Park. It aired on November 10, 2004.
For five long years, Stan, Kyle, Kenny, Cartman and Butters have kept a secret about an illegal incident that happened back in pre-school. Now, the kid who took the fall for the boys is getting out of Juvie and his first order of business is vowing revenge on the boys.
Stan, acting in panic, announces to the boys that Trent Boyett, a classmate from their preschool years, has just been released from juvenile hall. This causes the boys to worry and devise a plan to defend themselves from Trent's anger.
The boys recall the incident from their pre-school days. In their flashback, they get the idea of playing 'fireman', starting a real fire and extinguishing it. They just need someone to start it, so they ask Trent Boyett, the toughest kid in pre-school, who does. Butters advises them against, however, he is ignored. When the fire first starts, the boys urinate on it, trying to put it out. However, the fire gets out of control, and when their teacher, Miss Claridge, tries to extinguish it, she too becomes engulfed in the flames. Cartman and the boys then run over and urinate on her to try and put the flames out. Shortly afterwords, the police arrive and instead of taking what might have been the easier route by saying it was an accident and risking getting into trouble, the boys use Trent as their scapegoat - the boys lie and say they weren't involved. When asked by Trent, Butters refuses to speak in Trent's defense, as he feared he would be grounded for getting involved. Trent is sentenced to five years in juvenile hall, and the boys forget it ever happened until now, five years later.
Miss Claridge is burned so badly that she is forever confined to a sort of iron lung/motorized wheelchair, and she can only communicate by using an electronic beep: once for "yes", twice for "no."
Upon finding out about Trent's release, a desperate Butters plans to hide from Trent in his room indefinitely. His parents, Stephen and Linda force him to go out and play, locking him outside. Butters is caught by Trent, who offers him a five-second head start. Butters wastes two seconds, but then runs. When he is caught, Trent dishes out a brutal, bully-style payback, resulting in Butters being hospitalized. Meanwhile, Miss Claridge's motorized wheelchair runs out of juice and stalls in the middle of the street. Since her drained battery renders her unable to respond by beeping, the South Park townspeople assume she has become despondent.
To avoid Trent doing to them what he did to Butters, the boys go to the sixth graders for help. When they arrive at the hangout, the sixth graders say that they'll only defend them if they get a picture of Stan's mother's breasts. Stan, reluctant to ask his mother, even with Cartman's attempts to teach him how to reason with his mother, instead takes a photo of Cartman's buttocks with nipples drawn on them. The sixth graders fall for it, and agree to help them.
However, when the sixth graders tell Trent to stay away from the boys, Trent severely beats all of the sixth graders. Now, not only do the boys no longer have defense, Trent also knows they sent the sixth graders out to get him, which could possibly make him angrier. With no one left to ask, the boys ask Stan's sister, Shelly, to defend them. She agrees on the condition that they tell Miss Claridge that they were responsible for the fire, simply because she wanted to be the only one who beats the boys up.
The boys meet Miss Claridge, who is still stuck in the middle of the street and attempt to make peace with her. At this moment, however, Trent arrives to finish business. The boys try to talk with him, but Trent still does not want to settle, he mentions about the things he's missed out on such as a talking Christmas Poo and fighting a huge mechanized Barbra Streisand and adds that once his retribution is over, the matter will be solved for good. Once again instead of taking the easier route, Cartman takes out his mother's taser and fires it at Trent, however he misses, instead shocking Miss Claridge, recharging her wheelchair to such a degree that it goes out of control. The wheelchair spins in place then crashes into a propane shop, causing an explosion which destroys the shop and sets Miss Claridge on fire. Ablaze once again, Miss Claridge crashes into an hydrant, where the flames are put out. The police arrive, and since they already knew what 'Trent' did to Miss Claridge, they all thought he wanted to get rid of her for good. Trent tries to deny the fact, but the boys call him a liar.
The police ask Miss Claridge if Trent tried to kill her again. She replies "no" with two beeps; the police misunderstand think she means "Yes, yes", causing them to once again arrest Trent. The boys are saved, and relieved that they won't have to worry about this for another five years. Cartman goes on to moon and taunt Trent. However, he still has the nipples drawn on his butt. Just as he does this, the injured sixth graders come back from the hospital and see the whole thing. Cartman thinks he's in trouble, as the sixth graders might find out they tricked them. However, the sixth graders are once again fooled into thinking Cartman's ass is a pair of breasts. They grab Cartman, presumably taking him into "the bushes", similarly to what they did with the picture.