could it just be the lack of/inconsistent use of accommodations?
I'd certainly start with getting full compliance with the IEP, and then re-evaluating the school situation.
However, ADHD is comorbid with so many other things that I'd also want to know if it's present or absent. It often happens that even if parents don't think there is an issue at home, the child's needs have effectively trained the parents to modify the home environment so that "normal" at home is already structured to ameloriate attention or compliance issues. For this reason, when in doubt, I'm in favor of investigating.
There are now computer-based assessments of attention-- it's no longer just someone making an educated guess.
