There are 2 Disney Channel Original Movies in the 'High School Musical' franchise: 'High School Musical' and 'High School Musical 2.'
The first film premiered on Disney Channel on January 20, 2006, introducing Troy Bolton, Gabriella Montez, and the students of East High. Its success led directly to 'High School Musical 2,' which debuted on August 17, 2007, and became one of Disney Channel's biggest television events.
The franchise is often counted as having three movies because 'High School Musical 3: Senior Year' completes the original film trilogy. The important distinction is distribution: unlike the first two entries, the third movie was released theatrically in October 2008 rather than premiering as a Disney Channel Original Movie. Therefore, the franchise has three original live-action films but only two DCOMs.
Later projects can cause another counting mix-up. 'High School Musical: The Musical: The Series' is a Disney+ television series, not a DCOM, and it does not increase the number of DCOM movies. The answer remains two when the question specifically asks for Disney Channel Original Movies.