hermionc:

draco is definitely intelligent, at least in book canon!

• draco is a successful occlumens, apparently capable of shielding his thoughts from voldemort, one of the greatest legilimens of all time.
  
• he must have gotten high scores on his potions, transfiguration, and defense against the dark arts OWLs, as he managed to get into the NEWT level classes for these subjects.
• he’s skilled in non-verbal magic, which is supposed to be very difficult for young witches and wizards as it requires a high level of skill and concentration.
• draco was appointed a prefect for slytherin house in his fifth year. prefects are supposed to be exemplary students within their house, and likely get passable grades. although it’s mostly unknown how prefects are chosen, dumbledore explicitly tells harry he didn’t make him a prefect, which suggests that ultimately the decision resides with the headmaster. 
• he’s a talented duelist, even as early on as first and second year. by sixth year he can duel nonverbally, again very difficult.
• when he fixed the vanishing cabinet in sixth year, he did so using a protean charm - the only other known person of their age to have mastered this charm was hermione, as it’s a NEWT level spell which requires a lot of concentration.
• (this makes me sad but) draco was also very adept at preforming unforgivable curses - he managed to keep madam rosemerta under the imperius curse for almost a year, and he used the cruciatus curse on rowle. these spells are, again, very hard to master, and most adult wizards are unable to preform them with any precision. 

(all of this is from the harry potter wiki!)