My kids aren't far enough along in school to take AP classes yet, so no specific advice there - but fwiw, I second Grinity's advice - that's what we've had to do and what's worked for us in other situations where we've had to advocate for our kids at school.
You also might find it helpful to use some of the terminology that is outlined in the wrightslaw websites and books to prepare for a meeting if you have one. For example, they would recommend (as someone else above mentioned) - put your request for the meeting in writing. I think you could also find the wording there to address the issue of "we can't make an exception for your son because what if a whole bunch of other kids started asking to take AP History in 10th grade"... I am not that great with the words, but you want to reply essentially that "those other 10 million kids aren't relevant to this conversation. We're here to talk about my son and his educational needs."
Another thing you might want to do is see if there are any local parent advocate groups you can use for advice in your situation - we found a local advocate agency through the yellow pages at wrightslaw. The good thing about getting advice locally is that the advocate may have information about the ins and outs of your particular district and perhaps even the administrative staff at your school and they can also help you with advice on how to do/say what you need to in order to negotiate effectively.
Good luck!
polarbear
