Zac Efron's singing voice was that of Drew Seeley, who tested for the role of Troy. Seeley sang the entirety of "Get'cha Head in the Game" and the reprise of "What I've Been Looking For." Efron only sings the first four lines of "Start of Something New," the first sentence of "Breaking Free," and during the scene on the balcony. The reason for this is because Efron's natural voice was too low for that of a tenor and the producers wanted a tenor to match the role.
The film has its origins in a 1999 script entitled Grease (1978) 3. Britney Spears and Justin Timberlake were to star as the children of Danny Zuko and Sandy Olsson from the 1978 film. The plot was virtually the same as that 'High School Musical', but with more similarities to 'Grease'. The character who would become Sharpay was to be the daughter of Betty Rizzo (producers tried to get Christina Aguilera for the part, but she declined). Timberlake's band-mates from *NSYNC were to have supporting roles. John Travolta and Olivia Newton-John allegedly were approached for cameo roles. But before the script went through a second re-write, the project was shelved until 2004. They would also have had to get permission from whoever owns the rights to Grease.
In the beginning scene, the room where Troy and his dad played basketball was actually a room in the school where they shot most of the movie. It was actually a dance studio, but they covered the mirrors. You can see ballet bars in the back.
In Corbin Bleu's first appearance at the school, he was wearing three different watches. He was given a choice of which one he wanted to wear, so he chose all three of them. Each was set to different time zones.
Vanessa Hudgens had to compete with about 12 other girls for the role of Gabriella Montez during the callbacks for this movie. She and the other girls danced and sang all day to determine who would get to play Gabriella Montez.
Corbin Bleu was originally auditioned as Ryan Evans, but when he saw Lucas Grabeel dancing at the audition and said that he can't shake like Lucas can, and Ryan had to shake (when dancing). So, instead, he auditioned for Chad and was cast.
This was the Disney Channel's most successful movie at its time with 7.7 million viewers in its premiere broadcast. The record was beaten by The Cheetah Girls 2 (2006), which attracted 8.3 million viewers on its premiere night.
There are several noticeable attempts to set Troy and Gabriella apart from the people around them by placing them both in blue outfits. One strong example is the shot of Troy, the Wildcats, and the cheering fans seen out the window immediately before Gabriella sings "When There Was Me and You." At this point, Troy essentially looks like a blue spot in a sea of red.
"High School Musical" was just the working title for the film while a better name was thought up. However, by the time post-production came, a better name had not been thought of so the producers unwillingly went for "High School Musical"
Disney Channel executives and producers originally wanted Cassie Steele to play Gabriella after seeing her in another Disney Channel original movie Full-Court Miracle (2003). She auditioned several times and had a screen test, and was cast as Gabriella. However, the fifth season of her TV show Degrassi: The Next Generation (2001) seriously conflicted with the filming of this movie, so Steele had to drop out.
In its first week of release, the soundtrack to High School Musical debuted at #143 on the Billboard Top 200 and sold 6,500 copies. It went on to sell 4.1 million copies, making it the best-selling album in America in 2006.