B.B.
Write a letter to the school principal requesting that your child have a psych-educational evaluation. Check this site for a sample letter: http://www.ldonline.org/article/14620.
You want to note the date you sent the letter on your calendar and all responses from the school. They must follow a time line. You should get a Notice of Parental Rights which will outline everything for you. If the school is not responding and you do not get your copy of your rights, continue contacting them so they know you are serious. If you still don't get a timely response, look into an advocate. They are free and will help you through the process. Every school district is different. Some respond and do a great job while others will try to put you off as long as they can hoping you will just go away.
I was a school counselor and my husband is a principal. We also have a daughter who has Asperger's. The most important advice I have is to remember that your are your child's voice. Don't be afraid to make a fuss, often the loudest voice is responded to first.
Good luck.