I agree about about asking to include the challenge classes in the IEP.

I suggest searching the web for information about GIEPs. Here are a few links:

PowerPoint overview of GIEPS. This presentation provides a lot of good information about rights and responsibilities.

Tip sheet for parents

Sample GIEP

I think the most important thing you can do is to educate yourself about what's involved in writing a GIEP.

If they offer access to the class only via testing and he goes there next year, you'll have to let them test him. Personally, I'd ask them what will be on the test and would ensure that he can answer the questions.