After reading Finz's post I wanted to add a few last things, documenting functional limitations is very important as well. I also addressed Functional Capacity testing in one of the stickies last week, with links too, so please check my post out if your research predated my addition.

Also, I was unsure if your doc was stating that it was his opinion that "you're unable to work or attend school" or that he is simply relating what've you've told him. Stating that in his opinion you're unable to attend school or work due to pain and this is consistent with other patients in similar health, yada yada yada, would show he is in support of your decision. If you're going to hire an attorney, I would do that first before asking for anything specific from your doc, since your attorney might have a different strategy on how to address these issues.