Based on what I've read on the internet, it seems that it is assigned to people when the teacher checks the box that says, "Does not play well with others".
This is what WebMD says:
Asperger's syndrome, also called Asperger's disorder, is a type of pervasive developmental disorder (PDD). PDDs are a group of conditions that involve delays in the development of many basic skills, most notably the ability to socialize with others, to communicate, and to use imagination.
If this is a mental "disorder", then I would imagine that all of the Desert Fathers--many of them saints--has Asperger's syndrome. I've heard "late talkers" are often "diagnosed" as having Asperger's.
It does not seem to me to be something real, but the psychiatric industry can make a fortune treating it.
Some of the noted methods of treatment for Asperger's is "Special Education" and, of course, lots of different kinds of "therapies"; huge industries in themselves. Interestingly, the drug industry has not yet developed any pharmaceuticals to "treat" someone who is, essential, an introvert.