Firstly, welcome to AC.
Secondly, sorry for initially posting my last thought first. I was making notes, and accidentally hit reply too soon. I often radically edit my posts (as I have here) when working on my cell phone.
Do you know, or have you asked him, what causes him stress at school? Have you had feedback from the teachers? I'm assuming its more than not having friends, though that will contribute.
We've sometimes had other parents come here with problems with assignments. Teachers think they are being helpful by making assignment wording vague, allowing kids to take it where they want. But it just makes it impossible for aspie/autie kids to answer. They need something more concrete.
Maybe your son has comorbids like tics or Palilalia/Echolalia, or is uncoordinated, resulting in bullying or teasing? Or maybe the teacher is misinterpreting body language? If he has no idea of what is going wrong, it may be that he is making a social faux pas like always telling the truth, and is rejected for it.
Its hard to make recommendations without knowing his specific problems. Hopefully the doctor/clinician doing the assessment will give you some helpful ideas. Please also look around the resource section of the site for some book recommendations. If you have the time, I recommend reading Tony Attwoods 'Complete guide to Aspergers'.
What country are you in? Is there any chance of changing schools or even homeschooling? Personally, I think, homeschooling is a great option for most aspie kids.
Aspie kids need time alone to unwind. What activities does your son really enjoy?
As an aside... your son can't *be Aspergers* (probably not what you meant). He can *have* Aspergers Syndrome, or be an Aspie.