The high school referenced in the title is a military school for troubled rich kids. The school is on a remote island off the coast of California where the students, and for that matter the faculty, cannot leave. Mickey Rooney's son, who he hadn't seen for years, was sent there by mistake by his wealthy, now deceased, mother. His son died on the island and Rooney is there to find out what happened. Rooney, always a solid actor, actually has his best part in Platinum High School in an action sequence, where he fights three men using judo, empty rifles, and a knife.
Conway Twitty, Jimmy Boyd (I Saw Mommy Kissing Santa Claus), and Harold Lloyd Jr. are known as "The Three Beasts" and they show up from time to time during the movie to menace Rooney or to cause some other type of trouble. Conway Twitty has a few lines during each scene in which he appears. Maybe it was due to his Southern accent, but Conway's acting reminded me of Elvis during his earlier movies. I don't see any reason Conway couldn't have gone on to make more films if he had wanted, but I guess it didn't appeal to him as much as a music career. Conway doesn't sing in Platinum High School; however, he did compose and sing a great rocking tune for the movie's soundtrack (see below).