In the scene where Greg and Rowley are in the cafeteria (and Greg describes it as a terrible place), there is lettering on the back wall which appears to spell out "SH*T". Some of it is blocked by a pillar.
In the scene right before Rowley asks Greg if he "Wants to come over and play", Greg walks out, and you see a girl walking down the stairs behind him. When they show Rowley, the girl is again seen coming out of the school.