Why does it matter that it didn't say it was a graded assignment?? It was something that the teacher wanted a signature on and neither of you felt it was important enough to sign and send back.
I deal with 504's, IEP, BD,LD and every other learning issue in my school and I still don't understand what the 504 or the fact your child was "bored" have anything to do with the fact that the assignment *if you knew it was a graded assignment or not* was not turned in by the 9th.
I don't think you have a beef with the "young" teacher. I think you have a beef with your DH or yourself for not doing what needed to be done by the time it was supposed to be done.
Time for mom and dad to step up to the plate and take responsibility for NOT doing what needed to be done regardless if it said it was a graded assignment or not. If she had written graded assignment would your dh have found time to get it looked at and signed and turned in on time???
It's stuff like this that makes me

and so glad I stopped teaching!!