Continuity mistake: In the very beginning of "Go My Own Way," Gabriella starts to turn away from Troy twice; once in a shot from over Troy's shoulder and again when it is a side shot of the two of them.
Continuity mistake: During the final dance scene, "All For One," the sky in the background constantly changes from blue and cloudless to overcast.
Continuity mistake: During "Everyday" Troy's microphone keeps switching hands.
Continuity mistake: During "Work this Out" you see a girl pass by Taylor during the line "I don't remember you saying the boss is such a creep". The next shot you see the same girl move by closer to Taylor.
Continuity mistake: Troy's hair constantly changes throughout the movie.
Continuity mistake: During "What Time Is It" Jason is laying his head on his desk. His arms are change between shots.
Answer: It's a Musical. Instruments that aren't shown are always playing like this in these types of movies.