Find the critical books, articles, and other materials on autism and special education. Also, identify 10 key experts in the field, read what they have published online and/or in print, and consider contacting them personally as a resource, if possible.
Also consider keeping a journal for you and your child to record his experiences his strengths and challenges, artwork and summer camp certificates, and so on so that you can share it with new teachers, babysitters, and even relatives to help give a glimpse of your child's life.
When you encounter those who make rude or insensitive remarks, take the opportunity to change things for the better rather than taking offense or disregarding it. Every person you affect will affect others.