first, I think the sentence is very ill formed with wrong punctuation marks and is not a very good specimen of good english. I think it should be like this:
"He is the brattiest boy in the school: won’t listen, won’t do as he’s told, lounges at the back of the class all curled up, (has) insolent eyes and (makes) sarcastic comments until even, calm, rather weary, (and wears jumpers) ....<Some text missing> .... Mr Watson snaps and sends him to the head master."
Lounge means to pass (time) idly
the second part should be "Back of the class, All curled up !!"
So this means that he usually is lazying in a curled up position at the back of the class.
he passes sarcastic comments to get even with people, then stays calm and rather weary and can be distinguished by his jumper that he always wears
Now, I have tried to make sense of a very odd-looking paragraph and I am pretty sure this is not well written or punctuated. What is the source of this extract ?