Why the number of students is ambiguous

[pippin_999]

No: HPFGUIDX 86938

We've often wondered why JKR seems unsettled as to how 
many students there are in a House. 70? (7 years times 10 
students) 200? (The number of Slytherins at a Quidditch match)
250? (JKR's interview saying there are about a thousand 
students at Hogwarts). 

I think its ambiguous because she is skating her way around 
group dynamics. She doesn't want to have a dissident faction of 
Gryffindors, and that would be inevitable (in the real world) if 
there were hundreds of them. So Harry's house seems to be 
small.

 She does want there to be a dissident faction of Slytherins (the 
ones who stood to honor Harry at the end of GoF), and that 
wouldn't make sense if there were many fewer than one 
hundred. Dissidents would  then be perceived as individual 
non-conformists like Luna,  rather than a fraction of the whole.

But Rowling wants us to perceive that Slytherin and Gryffindor 
are the same size, as implied by the classes where there seem 
to be ten of each.   No wonder we can't get the math to work.

Pippin