"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.
After a failed attempt at a school field trip, which appears to have claimed the life of Üter, Edna Krabappel 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: Lisa becomes increasingly obsessive in her desire to be graded, 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 soaps, and Bart revels in his newfound afternoon freedom, 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's made, government budget cuts have squeezed the school dry.
Eventually, Marge is exasperated with the stalemate between the teachers and Skinner. She and the parents of Springfield eventually decide to take matters into their own hands by calling for a town meeting. Taking matters in their own hands, the parents chooses to recruit volunteers from the community to take over as temporary teachers. 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 children home for having his beard stuck in the pencil sharpener. This makes her worried more about not being able to get into her dream school. Bart becomes horrified when Marge becomes his new teacher, 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, Bart is the laughingstock 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 who whom tutoring has been quite successful, he tricks both Ms. Krabappel and Principal Skinner in to entering Skinner's office, which he then locks behind them. 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. Things 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).