Continuity mistake: When Napoleon is giving Trisha's mom the dance invitation you can see a car in the reflection on the door. Then when it shows the door again the car is gone.
Continuity mistake: When the uncle and Kip are eating at the restaurant, the uncle's onion rings continuously change position between shots.
Continuity mistake: When Deb comes to sell handycrafts to Napoleon, she has three boxes: a blue one, a red and white one, and a teal one. When Napoleon leaves his house he only has two boxes. But when he gives them to her at school, he has all three.
Continuity mistake: When Kip and Uncle Rico are in the diner, Rico's onion rings keep changing position.
Answer: Because it is such a small town that the school system can not afford buses for grade level so they have to share them, plus it has comedic value as well.
pross79
Small town schools are usually K-12. The other older "cooler" students drive to school or get ride with their friends.