It all started last year during a terrible thunderstorm, when I locked myself out of the house. Sheltering myself with a large piece of sheet metal, I ran for cover under the tallest tree I could find!— Homer
One of the staples of the Simpsons' opening credits is the blackboard gag. Bart writes something on the chalkboard as a punishment, quite often ironic. Here we list them all, including screenshots where useful. Any episodes not listed here do not have blackboard gags.
Season 12 starts 27th September.