Sardine, it might be that coming across a 'dirty mag' is in a whole differnt league than serious adult porn, for one a mag would be pretty tame in comparison to some of the things you could come across on the net.
Like when we found a set of playing cards with nekked women on them in a big book cupboard as youngsters, we were
at them, but mostly just interested in whose they were because our dad would never have stuff like that 
The OP though, I think the old line that some children know their rights and are as cheeky as fuck with teachers is true in some instances.
That's not the child or teachers fault, but the teacher has to have more power than children.
As a parent I want them to have more, and for the children to know that as an absolute.