I've found that NTs have trouble with any work that they find to be trivial and menial.
NTPs especially have trouble doing homework that does not appeal to their particular interests or pique their creativity/curiosity.
NTJs have trouble doing homework that they cannot see as directly useful to their broader aims/goals.
Usually, it's not a matter of being intellectually capable of doing the homework. It's a matter of being interested in the homework enough to let the homework take away from other tasks in which the NT could be engaged.
I know that I personally put off tedious work until the very last minute because I find that it takes away from the other things in which I'm interested. I know that it's necessary to do the homework to contribute positively to my grade in the class, but that's often not enough of a reason to put every ounce of effort into work that I find menial/boring.