Other mistake: A final contest is given for control of "green stamps" with all the kids building a "House of Cards." Whomever causes the cards to fall will be the losers. All is going well until Tiger comes in and knocks into Greg and causes him to bump the table and knock over the cards. If you watch closely at the end of the scene, when all the dialog is finished, you can see Mike trying to knock down a few remaining cards. However they keep popping up. Probably due to the fact that the cards were glued together to make it easier for the kids to build upon.
Other mistake: In one of the final scenes, Peter ignites his volcano on the patio in front of Marcia and the members of the Boosters Club. As the volcano goes haywire, Marcia and the Boosters are shrieking as the lava/mud covers them head to toe. Somehow Peter, who is much closer to the volcano, is unscathed by the eruption and remains free of any dirt.