When the hitmen arrive in the train station they take two cars, a Mercedes and a BMW. The BMW is a 5 Series (E39) which production began from September 1995. Since the action is taking place according to the school newspaper in May 1995, this car model isn't on the market yet.
In earlier scene in the class, Warren Blake wrote on the notebook:"If it's good enough for you, it's godunov for me." Later, when it was printed on the newspaper, it said:" If it's godunov for you, it's good enough for me."
When Giovanni is talking to the man at the sewage plant, the plant man's glasses are spattered with something. When he turns to the side, they're clean, and when he turns back to Giovanni, they're dirty again.
A high school student is said to be in the 12th grade. There is no such thing in the French system. In fact, the school doesn't remotely resemble a French high school. In its academics, social structure, cafeteria and even a school paper, it is merely an American high school transplanted to rural France.
At the auditorium when the movie Goodfellas starts, the line "as far back as I can remember, I always wanted to be a gangster" can be heard followed by the musical queue. Yet, this is not the opening line but rather "what's that noise?" referring to a man in the trunk of a car. The famous line by Ray Liotta isn't heard until the first minute of the movie.
French high school students are shown driving to school. The legal driving age in France is 18. High school (collège) ends at age 15. Even if the school depicted is meant to be a lycée (post-secondary university preparation - which a foreign student would be unlikely to qualify for), the students would still be too young to drive.
Fred visits a water tank with dynamite & a clock and wires the dynamite to the clock. However, he attaches one wire to the handle at the top of the clock and the other to the nut that holds the bell and handle on the clock. They are effectively the same piece of metal and the bomb should have exploded.
Throughout the movie, every person "The Family" encounters instantaneously starts to speak english and conversations take place in almost fluent english. This is very uncommon in France, especially in small villages like the one in the movie.
In the supermarket, Maggie hears the the shop keeper say:
"...Ils mangent des hamburgers matin midi et soir..."
which translates as:
They eat burger morning, noon and night.
However, it is translated on screen as:
"...They eat burgers for breakfast, lunch and dinner..."
which would be:
"...Ils mangent des hamburgers pour le petit déjeuner, le déjeuner et le dîner..."
The school publishes La Gazette. Serge's wife runs from the house and says:
"Serge. They've published your son's poem." He says that he'll read it on the plane. She hands him a folded copy of the paper yet when we see it resting on his chest while he sleeps on the plane. it is uncreased. Pristine. As though it had just come off the presses.