I don't know how much this will help, but wanted to share with you something I recently observed~
I volunteer in the school library at a time when there are tech classes going on. One of the students in one of the groups is autistic and their actions can affect the class as a whole. This student may speak out of turn a lot, off topic, become very distressed when their usual routine is disrupted, may take some of the picture books over to a chair to read while the teacher is instructing the group, and may start to cry over things which might seem easily-solvable or inconsequential to their peers.
This Monday, the special ed teacher spoke both to this students classmates about this student's autism. She preceeded the conversation with " First, we don't usually discuss students with other students, however, So and So's mom and dad both felt it was a good idea for me to talk to you about So and So." She went on to describe autism as a neurological disorder one never grows out of, that this individual perceives the world differently from a typical person, that some autistic students are extremely gifted but, when their routines are challenged, can be very upset. She also mentioned that the student "strongly identifies with being autistic" which, I think, gave that group some freedom to openly acknowledge this in a constructive way. The teacher addressed the fact that there were outbursts at times and that the student was in fact working on this.
I found that the conversation between these sixth graders was insightful, compassionate and thoughtful. One girl wanted to know how to be a friend during recess. Some other students had good questions about autism. By the time the conversation was over, I had a better understanding of this very original and quirky student and was so heartened to see the openness and acceptance on the part of other kids.
In my own child's second grade class, there is a student with autism (higher functioning) whose parents have not talked openly about this. I know this is hard for them, however, it is also very difficult for other parents because they do not understand 'why the parents allow him to act out'. Because I am not at liberty to share this information, all I can do is to offer some positive ways my son and other kids can help the child when those situations arise. This student is very intelligent and does tease other kids mercilessly--and won't stop when asked, but cannot hold his own when teased back. This creates a lot of conflict, sometimes resulting in physical harm. I truly wish that we could help our second graders to use better coping skills when this student starts to engage in unwelcome ways. As it is, we have a lot of angry parents and angry kids.
All of this to say, I think you should trust your inclination to share with those who might need to know. You don't say how old your son is, but if he's in school, do talk with the specialists there about how to open up that conversation. Little kids need very simple language ("oh, when you see Kiddo flapping his hands, this means he's excited") and positive explanations. Older kids and adults may need tools for "this is what works for us when X happens".
Hugs to you, you obviously care very much about how your child does in his world. I also wanted to add, there is a great manga series called With the Light, the story of a boy who is deeply impacted and his mother's experience of learning about his autism and connecting with him. Here's a link to a preview/review of the book. I found it very enlightening, realistic and hopeful:
http://autistscorner.blogspot.com/2009/09/autism-manga.html