Hi vafhj, welcome to PC
Well you could throw it right back at them (if you felt comfortable) with "Yes, I do forget school work at times, what do you suggest, how do/would you keep up?"
But............forgetting school related work (and anything else??) doesn't have to mean you've got a bad attention span..........maybe it's more that it doesn't interest you as much......so you're not as likely to absorb it as well.
So........can you do anything to make it more interesting e.g. a little imagination. For example put yourself in the place of........."in your head" substitute elements of fractions for something more interesting, that kind of thing.
And hey, you might want to think about some things that may not be helping too?? e.g. are you sitting somewhere which stops you concentrating so much, even right down to routines beforehand or if you're getting enough sleep. Even small changes can help sometimes.
And maybe try to get a "systems" together for remembering things e.g. make (more?) notes and check back on them, even read them aloud which can help; stick post-it notes around to help you remember specific things; even do some study with friends which could help............??
But if you find school work difficult, maybe talk to a teacher/tutor, who may be able to help a little with some things to make it easier??
But I hope this group of people aren't only throwing you criticisms??!! While this one might be helpful in leading you somewhere........make sure you're not only accepting/getting criticism, hey??
Alison