Though Kenny has reportedly "crapped [himself] to death," he can be seen sitting next to Cartman when Mr. Garrison enters the bus after kissing Kenny G.
Mr. Hat is on Mr. Garrison's hand just before he says goodbye to his parents, but is gone when he hugs them and walks out the door singing.
In the second POX advertisement for the recorder concert, it states that the concert will be held in Oklahoma City, Oklahoma, when it was changed to Arkansas.
When the camera position changes from back to front as Mr. Garrison approaches his parents' door, the direction of the rainfall doesn't change with it.
It is not remotely possible to play such a deep note as the low E on a tiny recorder, never mind any deeper ones.
Ear warmers are designed to barely dampen any sound as little as possible. They do not protect the ears from noise.
At the beginning when the class are playing the recorders, the music on the blackboard has a slight mistake. The first note in the second bar is a crotchet (quarter note) when it should be a dotted crotchet.
When four million children start to play revised music by Stan, Kyle, Cartman & Kenny, the 4 boys start to run to stop them. Meanwhile, Mr. Garrison and Mr. Mackey wonder if those are their kids but in the lower right corner Stan and Kyle are standing beside them.