The interior scenes were filmed at a Catholic private school: Juan Diego High School, in Salt Lake City, Utah. Notice all the posters on the walls, and careful camera angles - as many religious-based statues and framed pictures had to be covered up.
Ethan mentions that he had always wanted to be in a play. Lucas Grabeel, who plays Ethan, is also the star of the High School Musical film series, movies where his character stars in most of the high school plays.
The high school used in filming interior (and exterior carnival scenes) is located in Salt Lake City, UT - Juan Diego High School, a Catholic High School. Carefully placed posters and filming angles were necessary to obscure Cahtolic-related artwork and statues.