A clue nobody has brought up AFAIK...

[meriaugust]

No: HPFGUIDX 122185


Eric Oppen wrote:  
When Tom Riddle shopped Hagrid, and got him expelled, he had to have 
gone into the Gryffindor dorms.  Herself has said that Hagrid was a 
Gryff (I'd like it if some of the characters she obviously likes 
were put into _some_ other house...Hufflepuff, Ravenclaw, and, dare 
I mention, Slytherin, but that's another rant) and I'm quite sure 
that even someone as lacking in the common-sense department as Our 
Hagrid wouldn't have had an illegal-and-dangerous acromantula hidden 
outside of his own dorm. 

Meri now: 
Interesting theory, but IIRC Aragog himself says that he never saw 
any part of the castle except the basement room where he was raised. 
And in the diary scene I am fairly sure that Harry recognizes the 
dungeons where he has potions lessons as the place where Riddle 
confronts Hagrid. This isn't to say that prefects don't have acess 
to places in the castle that regular students don't (which only 
leads to the obvious question of where these areas are?) but I can't 
imagine them being allowed to go into other student's dorms. Just 
think: a hotly anticipated Quidditch match comes up and one house 
awakens to see its entire team turned into snails thanks to their 
opponents. That would open up a fairly large window for tampering in 
all kinds of things. 
Meri - thinking that the corridors are dangerous enough at Hogwarts 
without having to worry about being atacked by a rival in your own 
dorm!