When I see this kind of scenes I always wonder whether in Japan policemen actually routinely question people going about their own business or it's just a manga thing...
Moreover question people about things that aren't violations, to boot. Is there a law that students have to go to school that the police have to be involved? Not everybody there goes to high school, okay 99%+ but not 100%... And what if one simply lies "nosir, I don't go to school" what are they going to do? Call each school in the vicinity to check if such-and-such is absent today? Cops in Japan must have an awful lot of free time on their hands...