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: 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 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: 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 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.

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, Janice and Damian are in class talking about different things, like watching a movie, and Cady tells Janice she can't see her art show because she going to Madison etc., Cady is applying lip gloss. She holds a pocket mirror and in shots of the mirror you can see Cady holding the pink tube of lip gloss in the same hand, then when it cuts to wideshots, the tube isn't in her hand. The pink tube of lip gloss also has no lid on it, yet near the end of the scene a blue long lid appears on the pink tube.

Continuity: When Cady enters the dance after the Mathletes competition, her sleeve is down past her arms and we cannot see her hand. In the next shot, the sleeve is rolled up and her hand is visible.

Audio problem: When Janis shouts at Cady out of Damian's car, Cady says "It's not my fault you're like in love with me, or something.", and then after she says this, her mouth visibly moves to more words but no audio is heard.

Continuity: In the scene where Cady is starting her first day of school and her parents are saying goodbye, she starts to walk up to the high school. Her dad starts to walk away while her mom stays standing there. In the next shot where it shows Cady's face, her mom and dad are still watching her together.

Continuity: In the scene where Cady and Gretchen call Regina, without Regina knowing Gretchen is on the line, and then Karen is called, it is definitely night time outside the windows of Cady and Gretchen's. However, daylight pours in Karen and Regina's windows. They are all calling each other at the same time.

Factual error: The mall that the plastics state they are going to, Old Archard as stated by Cady, is an outside mall. However, the mall they go to is an indoor mall.

Continuity: When Cady is trying to get out of going to Madison, watch the level of her Dad's glass of water. From the first shot of the table to when he picks it up whilst saying "I think Cady's old enough..." the water level lowers.

Continuity: In the wake of the candy-cane grams, Gretchen's arms change from above her shoulders to on the desk.

Continuity: When the Plastics are explaining to Cady the "rules" at lunch, an extra in a red shirt walks directly in front of the camera, and then a couple of seconds later, she walks in front of the camera again walking the same direction that she was walking the first time she passed the camera.

Continuity: As Regina is about to write the things about herself in the Burn Book, as she flips to a new page we can briefly see the page about Miss Norbury on it, and it doesn't say "Ms Norbury is a pusher. A sad old drug pusher," but later on when Miss Norbury picks up a photocopied sheet of the same page, it does have the previous comments written in.

Continuity: On Cady's first day at her new school, she walks toward the front entrance through a crowd of kids. A Black girl with a green comb in her hair approaches Cady from the right and passes without incident. Yet in the very next shot, the same girl again approaches Cady and purposely bumps into her.

Continuity: In the Spring Fling scene, when Cady and Aaron are dancing, it alternates shots between Cady's face and Aaron's. Her arm is on his shoulder in one shot and the next shot it is on his arm. This happens a couple of times in the same section of that scene. Really obvious.

Continuity: When Cady comes home from her first day her father sets down his book on the notepad on the desk as he sees her. In the next shot as she goes inside the book has moved back.