If I read your posting correctly, the diagnosis of Asperger's Syndrome was made by all professionals via school district/county.  Has his pediatrician diagnosised him with Asperger's Syndrome?  How about a large teaching hospital (Children's Specialized Hospital) such as Stanford, NYU, etc.?  If you have only the school district/county diagnosis right now, I would definitely get a second opinion.  

We had a friend whose child had been "misdiagnosed" for YEARS by the school AND the doctor's as being ADD/ADHD.  Within the last two years, she was finally correctly diagnosed with Asperger's Syndrome.  Since the diagnosis,  she has been treated properly with both medication and appropriate teaching techniques used by the school.  She's now flourishing - after having spent so many years floundering.  Her self-esteem is improving instead of dwindling.

There is so much new information out there to help aid professionals in creating a proper diagnosis.  I would seek out professionals that have an understanding about these conditions and the minor differences that separate them.  Definitely don't return to your original doctor who prescribed a carnival of medications.  You need a fresh perspective!  

Might I suggest you call and visit with someone who is a specialist in the field of Autism?  I believe that they would have the most current information about Asperger's and could give you some great advice as well as a few names of trusted individuals your child could visit.  It's my opinion, that a SECOND opinion, would be very helpful to you, your child AND the school.  

A second opinion doesn´t hurt, but keep paying attention to the signs that you can see at home, because we, the parents are the best person to know how our children develop.
I understand that feeling. My son is finishing middle school this year and I was so scared when he started. First able make him feel comfortable. Let him know that he is going to be fine.
 The first day of school I went to school and I talked to the teachers and I asked them if they received his IEP, no one did, so I was so glad that I asked, because elementary school told me that they would know at the first day, but no.
Middle school didn´t want to give him a teacher aid, finally they did, but there was another problem, my son didn´t want to feel as a special kid with a teacher aid. My son is also ADHD. When we had an IEP we decided that the teacher aid was going to help him only when he was not focusing but she was not next to him.
I hope that your child has the same group of kids that he has now at elementary, that´s very helpful.
For me the most important was to talk to the teachers, remember they are our eyes in school, ask them for their email, and make sure to have an IEP at the beginning of the school year. My son had an accident at school because they didn´t pay attention when I told them that my son was asperger, after the accident they rushed with the IEP.
Now we are talking about high school even that I am nervous, I don´t let  him know. I just tell him you are on track, you can make it.
Just make sure to let him Know how great he is and make him feel confident about himself.
Good luck, and God bless you.