Continuity mistake: When Miss Trunchbull accuses Matilda of putting the newt in the water, the corner of the clock is visible at the top of the screen. You can see that the big hand is on the 5. At the end of the scene, the big hand is on the 2. Surely it didn't take 45 minutes for her to walk back to the desk, have the newt spilled on her, etc.
Continuity mistake: At the beginning, when Matilda is wiping her face, in the long shot the tap faces the left, but in the closeup it is facing the right way. (This is only noticeable on the 2.35:1 widescreen DVD version.)
Continuity mistake: At 1:03:33 It seems Matilda's hair is sweaty/wet at first but in the next shot when she and Ms. Honey crawl away from the Trunchbull's house, it's back to normal. (01:03:30)
Continuity mistake: When Matilda is reading near the beginning and her father says she's four, after she's talked to her parents, she walks away, and she's facing the door when her mum says that there's something wrong with her. When Matilda is having flashbacks to help her use her powers, she is still stood there, facing into the mirror whilst her mum says that. (00:08:32 - 01:09:02)
Continuity mistake: Near the end of the film, where Miss Trunchbull gets beaten with the erasers, she passes out on the floor of the classroom. As she lays there, Matilda causes all of the blinds in the room to rise. The character of Miss Honey can be seen watching them rise, but in the reaction shots she is shown looking down at where Trunchbull should be laying.
Continuity mistake: When Miss Trunchbull is chasing Ms. Honey and Matilda, the sweat stains constantly change between shots.
Continuity mistake: When Trunchbull teaches the class for the first time, the clock above the chalkboard reads 10 minutes to the hour. After approx. four minutes of filming, the clock now reads 10 minutes after the hour. There is no chance that the scene, depicting a single continuous event, would have taken 20 minutes.
Continuity mistake: In the scene where Miss Trunchbull charges Lavender, she has two boots on. She misses Lavender and falls through the door. The next shot of her, she only wears one boot. There was no time between shots that she could have lost the one boot and boots wouldn't just 'slip off' as she went through the door.
Continuity mistake: Matilda's eye colour changes from green to blue to brown to green again throughout the different ages in the film.
Continuity mistake: When Miss Trunchbull first walks out of the school doors, the children sitting on the steps in front of her and on the concrete sides of the steps get up and run off twice between shots. (00:22:30)
Continuity mistake: When Miss Trunchbull first walks out of the school doors, on Matildas first day, she walks down the stairs slowly, and in an aerial view she holds her riding crop in her right hand, down by her side. It then cuts to a behind shot of her and she is now instantly holding the crop with both hands, behind her back. (00:22:50)
Continuity mistake: When Miss Trunchbull is talking to Amanda Thripp in the school yard, watch Amanda's left pigtail. When she says, "You mean my pigtails?" Amanda pulls her left pigtail over her shoulder so it is in front of her shoulder. However, in the next shot the pigtail is behind her shoulder and in the following shot, it is in front again.
Continuity mistake: When Matilda's family is speaking out numbers and summing them up, the mum places a can of beer on the table that moves around between shots.
Continuity mistake: On Matilda's first day of school she gets off the car wearing a sweater and holding a notebook but them is shown just wearing her blue dress.
Continuity mistake: When Zinnia removes the hat from Harry's head after Matilda glued it, in one shot the hat is almost removed from the forehead but in the next shot the hat is still on it.
Continuity mistake: At the end when Trunchbull throws the boy out of the window, we see when he is flying back in that the brown car is parked about 6-8 feet away from the building and bushes. When Trunchbull runs out of the building to the car after having food thrown at her, the car grill is now almost touching the bushes and the car is further from the stairs. (01:26:00 - 01:28:00)
Continuity mistake: At the scene where Ms. Trunchbull is under attack by the children in Matilda's class, she tries to catch Lavender, a brown girl in purple dungarees. At the time Ms. Trunchbull runs into Lavender, both sides of her dungarees are buttoned. Then Lavender is lifted by Mathilda to hold on to a pipe at the ceiling. At the very single shot where she is holding onto that pipe you can see all side buttons of her dungarees are loose. (01:26:50)
Answer: The "real world" answer is that it's a movie, and without Trunchbull, there's no villain at the school for Matilda to battle. Within the context of the film, everyone, including the staff, is afraid of her and fear if they speak up, she'll retaliate.