When Matilda and Lavender approach their desks in Miss Honey's classroom for the first time, Lavender opens the lid of the desk and puts her hat inside. In the next two shots, the hat is clearly sat on top of the desk.
At the start of "Revolting Children", Hortensia's right sock is pulled up and her left sock is down. However once she exits the school building, her right sock is down and her left sock is pulled up.
Early in the movie, Miss Trunchbull is referenced as having competed at the Olympics after having also been the 1959 English champion in Women's hammer throw. This was not an Olympic event until 2000, making it unlikely Agatha Trunchbull competed at that level. Given the character, however, it might be presumed that it was all fabricated.
Despite the fact that Trunchbull despises pigtails (to the point she hurls Amanda Thripp out of the schoolyard by them), there are a few girls who sport the hairstyle.
Harry refers to tinkering with the speedometers of cars to alter their mileages. The odometer records the mileage, not the speedometer.