Actor Allusion: Taylor makes it quite clear she's attending Yale following high school. Interestingly, Monique Coleman has already attended, and she was even on the paper.
Adored by the Network: Disney Channel (at least in Australia) has a tendency to overpromote any of the films if it's set to air within a week. Almost every single commercial will have at least one ad about it. Considering that, at least between 2005 - 2010, the film aired once a month, this was quite common.
Dawson Casting: Many of the actors were actually in their early 20s, though when the films initially started, most of the characters were played by people close to their actual age. Taylor's actress, Monique Coleman, was 26 at the time of the first film.
Averted by Austin Butler in the spin-off film, who was nineteen and playing a college freshman.
Though she was raised in Texas and Utah and does not have to fake an accent so this trope is debatable.
I Want You to Meet an Old Friend of Mine: Prior to the first film, Olesya Rulin (Kelsi) and Lucas Grabeel (Ryan) had been in Halloweentown High together, as Natalie the troll and Ethan the warlock, respectively.
Incestuous Casting: In-Universe. One character remarks that if Sharpay could find a way to play both Romeo and Juliet, Ryan would be out of a job, suggesting that the two have played romantic partners in the past.
Romance on the Set: Between Zac Efron and Vanessa Hudgens, who were together for over five years. They confessed to liking each other during the first film and got together during the second. (Although they hid it for as long as they could to avoid media attention). Kenny Ortega admitted that he'd noticed their chemistry since the beginning, and deliberately paired them during auditions.