Revealing mistake: When Ed and Dexter are in the ventilation shaft, watch when they fall in the trolley thing. If you look carefully you can see Ed's wig hanging on the edge. It's got a good burger hat on it.
Revealing mistake: When Ed is in the good shake machine, if you look through the little glass window below him, Ed isn't actually in the good shake machine, since his shirt and nametag isn't seen here.
Revealing mistake: When the guy asks for a good shake and the weird kid shakes him you can see the people that work at the fast food restaurant moving back and forth very rapidly. This makes the shaking scene an obvious rewind and playback sequence.
Revealing mistake: When Ed is driving back to Good Burger from the date, he's turning the wheel a little bit, but if you look at the background, he's going straight.
Revealing mistake: At the beginning when Ed accidentally switches between the baby and the basketball, look closely in the background when Ed realises that he is holding a basketball, and the baby getting thrown through the hoop in the background is a doll.
Revealing mistake: Right after Dexter begins driving the ice cream truck, a stuntman has replaced him.
Answer: We don't know that he doesn't. He could simply go to a different school where the school year ends slightly earlier. It's also possible that he's already graduated or dropped out.
LorgSkyegon