Continuity: After the Halloween party, when Cady walks into Damian and Janis' house, Damian gets scared and tosses all of the popcorn out of his bowl. In the next shot of Damian his bowl is full again.

Continuity: When the principal is introducing Cady to the class, the amount of donuts on the desk changes between shots. In some shots there are two donuts on top of the donut box, and other shots there are no donuts.

Continuity: In the scene where Karen is explaining to Cady (Lohan) how her breasts can tell when its going to rain, you see a shot of both of them and Cady is beginning to smile/laugh, but then it cuts to just Cady and she has a straight face again.

Continuity: When the main character is confronted by her crush in her room, she puts her drink on a pile of CDs, the CD pile starts to fall in the background as there is a shot of the guy, a split second later the cup is on the table next to the CDs, and the CDs are piled differently.

Continuity: When The Plastics go to Regina's house for the first time, Karen walks over to the counter to put her bag down twice.

Continuity: When Regina becomes angry, and writes the horrible message in the burn book about herself to frame Cady and the others, the handwriting changes between shots. Look at "DO NOT TRUST HER" and "She is a fugly slut." - The handwriting changes noticeably, and "fugly slut" changes a lot - she writes it so the "g" and "y" have curled ends, yet it cuts to her sticking her photo in, and the ends to the tails on the "g" and "y" are straight. The line under "fugly slut," and the exclamation mark both change too.

Continuity: When Cady runs into her teacher on the first day of school and spills coffee all over her, look at Tina Fey's pants. It looks like she is wearing rubber pants when the coffee is spilling down her front. The color of the pants also change during this shot.