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: On the first day back after vacation, the exterior of the school is shown at 7:50 AM (wall clock over doors), with the sun's long shadows being cast facing away from the school. The day after Ms. Darbus overheard Troy and Gabriella singing with Kelsi, there is a voice-over of Sharpay screaming, "Callback!" just as the exterior of the school is shown. The clock reads 3:30, and the sun's long shadows are being cast facing towards the school, but we know that it's not even lunchtime yet. (00:07:50 - 00:37:55)
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)
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 Sharpay signs the audition sheet, while she's with Troy and Gabriella, her signature differs between the close-up and wideshot, and then again when Troy checks the sign-up sheet, while Ryan watches him. (00:12:35 - 00:17:50)
Continuity mistake: Things on Principal Matsui's desk change position between shots, and the cup with the ruler, scissors, etc. vanishes. (00:21:05)
Continuity mistake: On the second day back, when Troy takes his seat in homeroom, Troy's boxer's are patterned, but when he is trying to lose Chad as he runs down the stairs, his boxers are solid grey. (00:24:30)
Continuity mistake: When Troy tells Chad that he wants to catch up on some homework and then heads to the audition, he's wearing jeans with thick decorative white stitching above his right pocket (viewer's left). However, when Troy raises his hand and volunteers to sing with Gabriella, he is wearing different jeans - the decorative stitching above the pocket is gone. (00:25:00 - 00:34:50)
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)
Continuity mistake: When Troy sneaks backstage with the janitor's cart, he hides beside a camel. There are yellow tassels lying over the camel's sunglasses in the close-up, which are gone in the previous and following shots. (00:26:40)
Continuity mistake: After Ryan and Sharpay's initial audition, when Ryan tells the girl not to be discouraged because the theater needs fans, the blue janitor's cart is visible in the doorway. When Troy and Gabriella help Kelsi pick up the sheet music, the janitor's cart has vanished from that doorway, but when Ms. Darbus comes back to tell Troy and Gabriella about the call-backs, the janitor's cart has reappeared. (There are two doorways that have green exit signs overhead, at the back wall opposite the stage. Troy leaves the cart at the right doorway.) (00:33:40 - 00:35:40)
Continuity mistake: When Kelsi trips onstage, the only button on Gabriella's sweater that is buttoned up is the fourth one from the bottom, but when Gabriella runs up to the stage, the only button that is buttoned up is the third one from the bottom. (00:35:20)
Continuity mistake: At the start of "Stick to the Status Quo", when Zeke is singing, the nylon lunch bag opens and closes itself repeatedly, the brown paper bag is either upright or lying on the table, as well as other changes on the table that occur between shots. (00:39:30)
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)
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)
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)
Continuity mistake: When Troy is in the locker room with his teammates, Chad is handed the framed photo of Troy's father and there's a white sticker on the back of the frame. In the next shot, when Chad gives the frame to Troy, the sticker is gone. (00:58:50)
Continuity mistake: When Gabriella and Taylor walk through the cafeteria, Sharpay starts walking across the balcony to the stairs, cut to wideshot of the cafeteria and she is back at the center of the balcony with Ryan, motionless, but when it cuts to the next shot she and Ryan are already halfway down the stairs.
Continuity mistake: In the locker room scene where Troy walks in and his teammates confront him, Zeke describes the MVP in his picture, sits down, and puts the picture on the table twice.
Continuity mistake: During the speech which the basketball team gives to Troy, we have shots altering between Troy and Chad. When we see Chad, the two guys behind him are standing basically next to each other. When the scene cuts to Troy, the same two guys are now much farther apart (the right one of the two would be blocked by Troy if they stood as close together as in the previous shot).
Answer: I'm not positive, but that is what I've always assumed.