I've helped a LOT of parents through the 504 process (re: hidden medical disability) over the years, so I'm pretty familiar with both IDEA and ADA's provisions for plans.
That said, if you
can qualify under IDEA,
no question that is the best route to go.The only exceptions that I can think of are disabling conditions which require "management" rather than remediation/goal-oriented improvements, and are
anticipated to persist into adulthood without real mitigation-- in those cases, the child will need the protections of 504 in college, but still, cross that bridge when the child transitions out of IEP eligibility in middle/high school. These are persons for whom ADA is more appropriate, generally speaking. Learning is often
not the life activity most impaired in those cases, however.
Take a careful look at the qualifying conditions written into the law in IDEA. Many students with moderate impairments may not qualify under a full evaluation; but with learning the primary functional impairment, the odds are much better.
The real differences between the two things are in the fact that IEP's come with federal funds attached, that there is a very clear protocol for writing/review/procedural safeguards set forth under the law. It isn't
necessarily about the kinds of services or accommodations available, though strictly speaking "services" are only an option under IEP and not a 504 plan.
I'd request information from the Special Ed team regarding whether or not they believe that your child could qualify under IDEA. If not, then a 504 certainly seems reasonable-- but I'd want the IEP if it is possible. From a parental standpoint, there are much clearer procedural safeguards, and an IEP must be written with
measurable goals which are evaluated at regular intervals. (I say this as parent to a child with a 504 plan.)
ETA: Oh, and the evaluation criteria for both laws involves not comparison to levels of function, but
comparisons to the person's unaffected peers, which one could argue fairly successfully would not necessarily be "average chronological peers" in the case of a student with high cognitive potential via testing.
HTH!
