When Troy and Gabriella are singing 'Everyday', Troy spins Gabriella off and continues to do his own spinning actions, but he fails to sing his lines into the mic or even lip sync them. He also forgets about his mic for most of the song.
When Troy is sitting in his bedroom tossing his basketball up and catching it, you can her the noise a regular basketball makes when you catch it, but later in the scene, he squeezes it and you can see it is actually a plush pillow that would make no such sound.
When Troy and Gabriella are on the fourth fairway and the sprinklers come on, they are constantly rotating, steady-stream sprinklers. However, they are making the "ch-ch-ch-ch" sounds of impact sprinklers.
During the final dance in the opening song outside the school, Gabriella can be heard singing "ah, ah!" and everybody else sings "school's out, scream and shout!". But Gabriella is seen singing the words "school's out, scream and shout!" with everyone else.
During the song "I Don't Dance" Chad and Ryan sound like
they are singing during the part where they are all dancing near second base. But their lips are not moving, then when they face each other they are shown to be singing.
When Sharpay is telling her three girls by the pool about Troy and Gabriella taking over her show, when she looks up - the boom mic is clearly visible in the reflection of her sunglasses being help up in the air over the character.
When Troy is having dinner with the Evanses, the championship game from the first film is brought up, and Troy says, "Actually, my teammates here [referring to Chad and Jason, who are waiting on the table] stole the ball." In the game in question from the first film, Troy is the one that steals the ball, runs it down court and scores the winning shot, all by himself.
After the 'work this out' routine, Troy writes 'Let's go!' on his notepad. He then flips it down to be in Chad's view, and the writing is the right way up. He is seen writing on the front of the notepad. In order for the writing to have appeared the right way up in Chad's view after being flipped down, Troy would have had to rotate the notepad 180 degrees and would have had to have written on the other side of the paper. When he is clearly seen not doing this.
On the last number "All for one" right after the first chorus, where all the cast was singing on top of the cascade pool, they part their ways. Gabriella, Ryan and Taylor get down on the right, while Chad, Sharpay and Troy get down through the left. On the next shot, all the ladies are seen coming down on the right, while all the guys are coming down on the left.
After teaching the kids to play golf, Troy leaves and Sharpay hits a ball. Before she hits the ball, that is the only ball left. Then there is a closeup on the ball and there are two balls behind it. Then when it shows Sharpay hit the ball, there is a pile of balls and one set off to the side for her to hit.
When Sharpay and Ryan are watching Troy and Gabriella dance and play around on the golf course, Ryan's binoculars are on his right hand, then they're gone, then they're on his hand again. The light in the scene keeps changing too.
When Troy and Sharpay are rehearsing You Are the Music In Me, Troys hair is blowing up while both of them are standing on the vent. Then the camera switches angle and Troy's hair isn't blowing up anymore, its straight down like there is no air blowing on them.
The reflection of Troy during 'Bet On It' does not match the shot afterwards. The buttons on his polo shirt are on the left in the reflection but in the 'real' shot afterwards the buttons are also in the left when they should be on the right.
During All For One, the number of balloons in the pool changes. First these is a cluster of 4 in front of cascade area, which then increases in number to approximately 10. The number varies between about 4 and 10 during the entire dance number in front of the pool. When the Troy and Gabriella return to the top of the cascade pool, the balloons have disappeared completely.
During the song "You are the music in me" Gabriella's tongue is clearly blue in some shots, yet when she sings a long note later, her tongue is magically clean again... A few seconds later, it turns blue again!
When Ryan and Sharpay arrive, Mr. Fulton shows them the fliers. There is one pile and he takes one off for Sharpay to sign. When it shows an up close of her signing there are already two or three fliers underneath the one she is signing.
During the final musical scene when they are dancing around the pool, the sun is getting low in the sky. During a close-up scene, the sun is high in the sky. In the last scene they are dancing in the late afternoon sun. Seconds later when they all jump in to the pool it is so dark that the area is being illuminated by electric lighting equipment.
Just after Troy asks Chad to put a swiss on his burger, Ryan is standing behind Troy with a tray of burgers. When Chad gets into the kitchen and talks to Taylor and Gabriella, Ryan is in the background with dirty dishes.
When Kelsi gives Troy the staff letter there is a plate in front of him with a croissant and a pancake on. When he screws up the letter in the close up shot, the plate has disappeared. It reappears when he leaves to sing "Bet on it."
When Sharpay and Ryan are singing their parts in the middle of "Fabulous", after she raises her arms while she is sitting on the piano, her left pink coat sleeve is fully on her shoulder. When the close-up shot is on Sharpay, her sleeve is completely off her shoulder.
When Sharpay is talking to Ryan at her locker at the beginning of the film, she puts her sunglasses on. but when the shot changes to outside of the school, Sharpay comes out without her sunglasses off and they are no where to be seen.
In the opening song of "What Time is It" Troy and Chad and various other characters are doing choreography with the basketballs, it is clearly seen that someone in the back dropped their basketball. But in the next frame of that scene the ball is gone and back in someones hands.
When Troy invites Sharpay up on stage during 'Everyday', she joins him on his left at the right side of the circle, with Gabriella and Ryan at the top. The camera them pans out and zooms in but Sharpay is on Troy's right and they are to the right of Gabriella, not the left.
In 'Gotta Go My Own Way', Gabriella's hair is styled one way during the first verse and the chorus. Then, when she goes to her locker, you can see that her hairstyle is different; it has more "volume".
When Gabriella is seen singing "Got To Go My Own Way" the 'T' necklace given to her by Troy is around her neck. When she is seen in the locker room, it is gone. When she is seen walking to the van she is wearing it again. But then she hands it to Troy when she leaves for the final time. We never see her take the necklace off.
After Troy has dinner with Sharpay's family he goes into the kitchen and screams. He then looks at a non-existent watch on his wrist to see that he's late for his date with Gabriella. This is a reference to the "watch" goof in High School Musical.
When Gabriella is seen singing "Got To Go My Own Way" the 'T' necklace given to her by Troy is around her neck. When she is seen in the locker room, it is gone. We never see her take the necklace off but we also never see her enter the dressing room. It could be that she took off the necklace upon entering the locker room.
During the song 'Bet on It', we see Troy looking into the water at his refection, however the reflection is not flipped like a reflection should be as you can clearly see the buttons on his T-Shirt are on the left, when we look back at Troy splashing the water, the buttons are still on the left.
After "I don't dance", Ryan and Chad are sat on a bench about to eat lunch. The mountains in the background are dark revealing that this scene was filmed at night and a stage light was used to give the illusion of afternoon sunset.
The goof items below may give away important plot points.
When Gabriella breaks up with Troy during 'Gotta Go My Own Way', she gives him back her T necklace. Yet when she surprises him during 'Everyday', she's already wearing the necklace again. How did she get it back?
In the baseball sequence Ryan's team was the home team and Chad's team was the away team. In this scene Chad hits final hit brings in runs to win the game for his team. In actual baseball Ryan's team not Chad's team would have had their last ups before losing.