Corrected entry: When the children first go to school, the teacher says "welcome to 7th grade." Later, he asks them a question and Trevor McKinney says "because we're eleven." Children entering 7th grade in the United States would be at least 12 (a child must be at least five years old in September to enter kindergarten that year, 6 to enter 1st grade, etc.). There may be some exceptions - a child who skipped a grade could be 11 though it's more likely to find a child held back a year at 13 - but since he said "we're," it could be assumed that most of the children are the same age, i.e. 12 going on 13.
Corrected entry: Near the start when Haley Joel Osment first meets his new teacher, there is a close up of his face when Mr. Simonet is speaking. It is around when he tells the class their year long assignment. In the background there is a kid from the class mouthing the exact words that Mr. Simonet is saying.
Corrected entry: In the end of the film, where Haley Joe Osment's interview is shown, you can see the wise words Mr. Simonet wrote on the black board in the beginning, but erased in the middle of the film. Suddenly it's back in exact the same place.
Corrected entry: When the boy is sat on the white bench asking the teacher why he hasn't called his mum and that he needs to be there when his dad returns. You see the boy drop the pencil he was using to cross out the 3 names of people he tried to help, by his feet. It lands on the bench where his feet are. In the shots following the pencil is gone.
Corrected entry: when the kid runs away and the mother is desperate to find him, she tells the cops on the phone "if I had a car I'd be out finding my kid myself" we know from earlier scenes that the bum fixed her truck and so she does have a car.