"The PTA Disbands" is the twenty-first episode of Season 6.
Bart pushes the teachers to strike. Local Springfieldians take over the teaching positions, so Bart must find a way to improve relations between the teachers and Principal Skinner.
The students of Springfield Elementary are on their way to their field trip at Fort Springfield. Unfortunately, the bus is falling apart, as the floor is breaking up, the bus is moving unstably and the brakes aren't working (the kids had to use their jackets to stop the bus). Bart and Milhouse are relieved they didn't take the other bus, which blows up after a leaf falls on it. After they arrive, Skinner has to pay for the trip up front, but the amount for students is more than Skinner has, he says no school could afford that, however he is proved wrong when a better school is able to go in. They decide to just look over wall, unfortunately they are caught "learning for free" and they make a run for it. After the failed attempt on the school field trip, which appears to have claimed the life of Üter, Edna Krabappel tries to tell Skinner that by not fixing the school, the kids are losing their futures, Skinner accidentally, out of anger, says that that the kids have no futures, which shocks everyone. From the busted school bus to the terrible cafeteria food to the cheap school supplies, the teachers are fed up. Edna calls an emergency strike on behalf of the Teachers' Union of Springfield Elementary, to protest Principal Skinner's miserly spending on school supplies and activities (namely because the government had cut their budget, and he needed to use half of the school's budget to fix the exhaust leak on the already hugely in disrepair bus) after being manipulated by Bart.
The various student characters respond to the sudden turn of events in their own ways: while most of the kids play in the streets or go to their favorite hangout spots, Lisa becomes increasingly obsessive in her desire to be graded and to learn, Milhouse is forced by his parents to take private tutoring lessons and it helps him improve, Jimbo finds himself immersed in the intricacies of daytime soap operas, and Bart revels in his newfound afternoon freedom, causing mayhem, which eventually irritates Marge and the neighbors. In particular, Bart does what he can to keep the union and Principal Skinner at odds with each other. The two sides are at an impasse, the union wanting a restoration of funding and Skinner maintaining that even with the spending reductions he has made, government budget cuts have squeezed the school dry.
Eventually, Marge is exasperated with the stalemate between the teachers and Skinner and also the fact that Lisa and Bart need school to grow. She decides it's time the kids back to school. The PTA does an emergency meeting where Mrs. Krabappel says that the students deserve better learning materials. However, Principal Skinner mentions that the only option is to raise taxes. Unfortunately, it is still a stalemate but Ned Flanders reveals that the PTA has a plan: use robot teachers, or if they are not around, use people from the neighborhood. This turns out to be even worse for the students than before the strike, especially as Jasper becomes Lisa's new teacher and sends the kids home for having his beard get stuck in the pencil sharpener. The other teachers aren't any better even Professor Frank who teaches the kindergarten class with a familiar toy and explaining the science around it. Bart becomes horrified when Marge becomes his new teacher (it was thought at first that a muscular man was their new teacher but he was only coming in to introduce Marge to the class), after Skinner learns that he scared away previous substitute teachers and planned to use her to keep him in line. Due to her excessive mothering of him as well as her embarrassing him in front of everyone, Bart is the laughing stock of his class, which Nelson and his friends takes advantage.
Fed up with Marge being his teacher, Bart grudgingly resolves to force the strike negotiations forward. Together with Milhouse, he tricks Krabappel and Skinner in to entering Skinner's office, which he then locks behind them. He then tells them from outside that they are not leaving until they reach an agreement on this entire thing. After spending several hours trapped together "like prisoners" in their own school, the two are mutually inspired with an idea to create extra revenue for more school spending. Matters return to normal with the old teachers in charge; however, the school classrooms have been rented to the Springfield Prison. Each classroom now features several full prison cells at the back, which have the added benefit of keeping the more troublesome students in line (although it is clear from the last line that Bart intends to help free Snake Jailbird, who is in the cell directly behind Bart's desk).