Betty Buckley really slapped Nancy Allen across the face during the detention scene. Brian DePalma wanted the right reaction.
Director Brian de Palma originally wanted Sissy Spacek to play Chris Hargenson (now portrayed by Nancy Allen). But Spacek wanted to be the star, so she showed up for her audition in a dress her mother made for her in 7th grade. She looked so awkward and hopelessly out of touch with fashion that De Palma cast her as Carrie.
Brian De Palma was casting the film at the same time George Lucas was casting "Star Wars." Sissy Spacek was considered to play Princess Leia, and Carrie Fisher was considered to play Carrie.
In a deleted scene, Carrie causes small rocks to rain from the sky. Huge boulders were supposed to rain at the end of the film when the house collapsed, but the machine that sprayed them jammed. So the filmmakers decided to just burned the house down instead. However, they had already filmed the indoor shots with the rocks coming through. But somehow they got away with it.
The boy on the bike that yells "Creepy Carrie, creepy Carrie!" is Brian De Palma's nephew Cameron.
The voice of the little boy on the bike who yells "Creepy Carrie. Creepy Carrie." is Betty Buckley's voice.