Continuity mistake: When Glad Hand is telling them about the get-together dance at the gym, you can see A-Rab putting his arm on Action's shoulder, then in the next shot he does it again.
Continuity mistake: When the gangs are fighting in the playground, in the aerial shot you see that two of the seesaws are pointing up away from the gangs. When the Jets leave a few minutes later, all of the seesaws are pointing up away from where they were originally. (00:14:16 - 00:17:39)
Continuity mistake: At the dance, when everyone is swaying with their partner, you can see both of Ice's hands on Velma's back, then in the next shot when it's following baby John, you can see Ice put his hands on her back again. (00:32:30)