Hmm... this isn't really a goof, more of a story oversight...
Dewey's moved to the Busey class in 5x18, so logic would have it he's still in that class for 5x19 - but in 5x19, Dewey's "class" are supposed to be selling chocolate bars. Given how the Buseys are treated and that they're given hardly any opportunities - Hanson is even rebuked for "learning something" - how likely is it that they're asked to go knocking on neighbours' doors selling candy bars?
I know it isn't important, but it was annoying me.
That's not a flying chocolate maker.
(Dewey in Halloween Approximately)
It's not lying if what you're saying would be true if the facts were different. (Hal in Tiki Lounge)