Oh, this discussion is hitting close to home. DD9 was a DISASTER about finishing/getting to homework last year - and I tore my hair out trying to get her to just start, and then finish it all year long. When her G&T class started she was also clearly getting MORE homework than she had previously been getting. I'll admit, some of the homework WAS horrifically boring or busywork...but still. DD might be a tad ADD-ish herself when it comes to homework (excellent PSI, but much lower WM/average than reasoning; no Dx, though; always been strong-willed and a tad impulsive) - although the teacher described her as always "working so hard" at school (hmmm...I always wondered about that). Then she'd get home. She wanted to do ANYTHING but focus on what needed to get done. I tried letting her get to it later, but then she turned into a puddle. I tried making her start earlier, but she seemed to have no focus left (she left it at school???). We always got it done, but it wasn't pretty.
She absolutely does NOT manage her time well. At all. I don't know that grades will motivate her - that is not WHY she has ever learned anything. She learns things because they interest her.
I honestly think part of it is DD needing to "contain" herself at school (be less DD-like to "fit within the confines of school") - she seems to have no discipline left when she gets home for homework. I am glad she is trying to um, "fit" a bit (she couldn't contain herself very well when younger and we'd occassionally hear about it), but she has no patience left when she gets home.
I am seriously thinking of establishing a reward system with Minecraft time (both DC are obsessed, but I limit it - and I admit to using it as a carrot) for getting her work done in a reasonable amount of time this year...I need to come up with SOMETHING.