By the way - a 504 is to cover accommodations for a MEDICAL diagnosis. The child's grades should not be a factor in the matter.
Just because a kid with terrible asthma is getting A's, doesn't mean they don't need a 504 for accommodations regarding physical activity. Just because a kid with PTSD gets A's doesn't mean they don't require accommodations. Same for ADHD! If you want a 504 you need to submit a request, in writing, asking for an evaluation.
Personally, I would want to go into the ARD meeting (or whatever they call the acceptance meeting where you live) with paperwork in-hand from a private neuropsych or psychologist.
