Continuity mistake: When Troy and Gabriella are singing "Start of Something New" Gabriella's left sleeve moves up and down between shots during the scene.
Continuity mistake: We see a close up of Gabriella slipping in some milk, but in the wide shots there is no milk or carton on the floor. (00:41:30)
Audio problem: When Troy and Gabriella are singing "Breaking Free" for the last time, Gabriella moves her mic away from her mouth numerous times, yet her voice never gets quieter.
Continuity mistake: When Troy tries to ditch Chad to go to the musical audition, he is wearing a belt (as seen when he is going down the school stairs) and white tennis shoes (as seen when he is almost caught by his dad when he rests against the side of the building). However when he makes it to the audition he is now wearing navy blue tennis shoes and no longer wearing a belt (as seen when he "volunteers" to sing with Gabriella). (00:25:15 - 00:35:00)
Audio problem: In "We're All in this Together", you can hear either Troy or Gabriella's voice singing background, not matching the others' lyrics, but their lips are moving to the same words as all the others.
Other mistake: During the musical auditions, the pairs audition doesn't start until halfway through the auditions. But the disturbing dancers were a pair audition and Ryan and Sharpay were the only pairs.
Continuity mistake: When the cheese fries land on Sharpay, they are all standing right beside the staircase (there are three levels of ledge at the base of the staircase), with Jason and others on the ledge by the banister. Then Sharpay screams. Next shot is of Martha standing atop her table, with the staircase and ledges visible behind them, as they all look to the right, as if Sharpay is farther off in the cafeteria. Problem is that Sharpay, Ryan, Jason, and all the others have vanished, though they all should be right beside that staircase behind Martha's table. (00:43:20)
Visible crew/equipment: At the start of the first shot in Principal Matsui's office, when Ms. Darbus and Coach Bolton are arguing about detention, the camera's reflection is visible on the computer screen as it's tracking backwards. (00:21:05)
Continuity mistake: In homeroom, on the first day back, there is a black pen lying on Taylor's notebook that flips itself around and also vanishes and reappears repeatedly between shots, during the cell phone menace scene. (00:10:10)
Revealing mistake: In the cafeteria scene, when Gabriella slips in the spilled milk, her tray is not only shot up, but tilted as well. However, after the camera cuts back to Gabriella, there is a cup of "sauce" yet it doesn't slide or tip off the tray.
Continuity mistake: When Troy's mom tells Troy to get ready for the party, his dad gives him the basketball. In the next shot his dad is still holding the ball. (00:01:15)
Continuity mistake: In the homeroom scene, Ms. Darbus says "Mr. Bolton, I see that your phone was involved so I will see you in detention." and we see a close-up of Troy with both of his hands resting on his cell phone, with one hand ready to close the phone. The camera angle zooms out, and, instead, we see one hand resting on his lap and one hand holding the phone. (00:10:10)
Continuity mistake: When Gabriella is shown Troy on the laptop, dismissing the musical, she begins to cry. She still has wet tear streaks on her face as she looks out the window, but as "When There Was Me and You" begins, her face is dry.
Continuity mistake: When Troy and Gabriella exchange numbers, Troy uses Gabriella's phone to take a photo of himself, but he doesn't press enough, if any buttons to put his number in.
Other mistake: When Sharpay is looking for Gabriella in the girls bathroom, she walks past where Gabriella is hiding behind the wall. It is also shown that there is no other room behind that wall. When Sharpay turns around to walk back out, it is impossible that Gabriella couldn't have been seen by Sharpay as she would have been in direct line with her vision. (00:48:45)
Continuity mistake: Things on Principal Matsui's desk change position between shots, and the cup with the ruler, scissors, etc. vanishes. (00:21:05)
Visible crew/equipment: When "Stick to the Status Quo" is starting, the camera pans down from the balcony past Sharpay. As it goes down, you can see the camera reflected in the balcony's glass screens.
Continuity mistake: The post-callback basketball scene's countdown clock isn't accurate. If you try counting with it, you'll notice that it reaches 0 by the time that the ball's being passed to Troy.
Continuity mistake: When everybody is exiting Ms. Darbus' classroom after the first day back, as Troy and Gabriella talk in the hallway, some of the same people are seen walking out of the classroom twice.
Continuity mistake: During "Stick to the Status Quo", when Martha is singing, things on the table change/move around between shots, particularly the milk carton to her right, which has two straws, then none, then one, then none, then one again. (00:40:00)
Answer: I'm not positive, but that is what I've always assumed.