Chester is talking to Matthew from the van and Matthew is holding a football. A teacher asks Matthew if he is all right and we see Matthew holding his backpack and not the football. Earlier, Matthew left his backpack with his friend, who threw him the football.
When Chester is thrown out of the bar, it goes from day (interior shot) to night (as he is thrown on the sidewalk).
About 52 mins in, Chester & Julie are singing "Great Balls Of Fire" with the soccer team in the minivan. At first, you see Matthew/Martha in the 3rd row of seats on the right side of the screen but at the end of the scene, Matthew/Martha is in the 2nd row of seats between Chester & Julie in the front.
At the final game, some of the "girls" on the opposing team are clearly male actors wearing long curly wigs.
In the first soccer game Matthew/Martha plays there are several full body shots of him running and kicking the ball and especially the shot of him kicking the ball into the net for a goal where you can see the face and it is obviously the stand in and not Jonathan Brandis.
Rodney Dangerfield can be seen mouthing the lines of other actors.
During Matthew's dream sequence, when he and Kimberly are served two hamburgers on a silver platter, one of the hamburgers has two top buns.
When Chester and Matthew argue about the team, a boom operator is reflected in thecar door as Matthew closes it.