12 year olds believe lots of silly things, I'm sure.

A different but related point that I find a bit unrealistic at various points in the series, but especially here, is how the older students are often depicted as reacting much the same way as the students of Harry's own age. I mean, seriously, imagine you're a 17-year old student in that situation. Are you really going to take the idea seriously that some 12-year old, albeit a notorious one, would be capable of doing these things that you yourself have no idea how to do?

The Quidditch teams sometimes suffer from the same problem - that Malfoy manages to make lackeys of the Slytherins in his own year, okay, sure. That he manages to buy his way onto the team through those broomsticks, I can buy as well. But it does not make sense to me that they'd act so subservient to him, when most of the people on that team have to be three, four or five years older. That's an enormous gap at that age, they should barely be giving him the time of day, famous family or not.