Simon Brew writing for Mental Floss:
In Philip W. Errington's biography on Rowling, he wrote that Levine wanted “a title that said ‘magic’ more overtly to American readers." Levine was concerned that Philosopher's Stone would feel "arcane," so one of the proposed alternatives was Harry Potter and the School of Magic, which Rowling shot down. Eventually, the author suggested Sorcerer's Stone, and that's how the book is known in the U.S. market where Scholastic had the rights.
I am relieved it wasn't called Harry Potter and the School of Magic. However, I'm still partial to Philosopher's Stone, and it annoys me that the movie's called Sorcerer's Stone, and that in the U.S., they never reverted to the original title.