Trivia: Tim Meadows, who plays Mr. Duvall, broke his wrist a week before filming started and had to wear a cast. They explained this away in the movie by saying that Mr. Duvall had carpal tunnel syndrome.
Trivia: Amy Poehler, who plays Mrs. George, is only seven years older than her on-screen daughter Rachel McAdams, who plays Regina.
Trivia: Lindsay Lohan originally wanted to read for the role of Regina.
Trivia: An interesting fact that I was able to confirm was purposeful by watching the commentary on the DVD- Tren Pak, the popular Asian girl who makes out with Coach Carr, is the on-screen sister of T. Pak, an Asian nerd on the Mathletes (same Asian nerd who says Regina's hair is insured for $10,000.).
Trivia: Lindsay Lohan was originally cast as Regina George. She thought the role would be different than her previous "damaged teenager" characters. However, according to the casting director, Paramount wanted a "bankable" actress for the starring role. Lohan was switched with Rachel McAdams, who had been considered for the role of Cady.
Trivia: A well-known actor, whose name has not been revealed by the director, was first chosen to play Aaron Samuels. He was fired after he came to the table reading with a messy, unshaven appearance, mumbled a lot, and refused to take his hat off. The actor is sometimes rumoured to be James Franco, but Daniel Franzese (who played Damien) has denied this.
Answer: Precisely because he was sleeping with a student. Getting her pregnant would bring their affair out into the open and create a scandal for the whole nation to know what he was up to. Therefore safe sex was really important to him.
The_Iceman
True, but since he was spending time with her, he could make sure that birth control was being used (i.e. him using a condom). I think he was trying to appear "uptight" about sex, so he could be the least likely suspect.