Ashley Tisdale who played Sharpay Evans is a natural brunette in real life. 

 Ryan Evans is dyslexic. He had trouble reading that G-O D-R-A-M-A C-L-A-S-S sign, when some of the Wildcats came to show support for the school's drama class.

 All the HSM movies were shot on actual location of an high school at Salt Lake City, UT That's a Mormon capital of the world. 

  Zac Efron's voice was going through some typical male teenager's changing phase when they shoot the HSM1, so it wasn't good enough for Disney back then. That's why they got another guy, Drew Seeley, who did all the singing in that first movie. Zac did all the singing parts all by himself in the sequels, in HSM2 and HSM3.