Continuity mistake: When TJ makes the morning announcements, in the first scene of the classroom we see a boy in a blue hat sitting in the back row. After TJ says that the kids can refuse to answer a teacher, the same kid is suddenly sitting in the second row so he can slap hands with someone in the first row.
Continuity mistake: When TJ announces that there will be no gum sharing, it shows Gretchen in the classroom. There is a kid sitting behind her. However, this is the same kid who is caught running in the hall, who Ms. Lemon says is a sixth grader. The gang is in fourth grade.