"A high school teacher's unusual experiment to demonstrate to his students what life is like under a dictatorship spins out of control."
Firstly, I'd like to comment about the annoying American subtitles - especially as more people will probably see this in my local movie theatre than in the whole of the United States. At one point "comedy club" was translated as "Saturday Night Live". Eh? Seriously, eh? It's even more annoying as the film is brilliant and a US remake is inevitable.
The Wave is actually based on a real-life incident in the late '60s in America but the point is that it can happen anywhere at anytime to anyone. While there is a theme and a point of view, it's actually quite subtle and non-preachy - you just get lost in the story as the tension builds to the great ending.
It's psychologically true and you understand the motivations of every character. There are no heroes and villains although people do brave things and bad things. I particularly admired the speed, skill and economy of establishing the characters.