I did it twice and it ended up differently each time. Both scenarios involved people who had experiences with others on the spectrum.
When I admitted to it for the first time, I did so because I knew they thought that disabled people are normal people too. It went well, truth to be told I didn't feel that they treated me any differently than before. They paid attention to my requests and suggestions about what I would need to work better long before they even knew I had a PDD and ADHD!
They just figured that all people need different things and did their best to respect that and accommodate to it. Amazing people, they were like that to their special ed students, their regular ed students and many others.
The other time I didn't do it myself and I regretted that they knew. When a problem occurred, I somehow ended up with a lecture on social skills. I felt silly discussing that because the situation on hand was unrelated to my autism beyond that of course, I am always autistic and some people might plainly not accept me/a young adult who is "different".
Worse than that was the impression that they tried to pin the problem on me having autism, even if not intending to do it. I'm sure they didn't, they're great people, but prejudices are common even in specialists for the spectrum after all.
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Autism + ADHD
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The trouble with having an open mind, of course, is that people will insist on coming along and trying to put things in it. Terry Pratchett