Yet another also in the US and can't speak for the UK. But I was tested and diagnosed as an adult for both Aspergers and ADD/ADHD. Neuropsychologists do the testing. I've been tested 3 times for ADD/ADHD (depending on the neuropsych). They used questionaires of childhood and adult experiences and very extensive word memorizing/recognition lists to look for inattentiveness. The last neuropsych I saw also administered two different very lengthy computer tests to measure attention span. hee hee and I failed miserably. I think its very definitive testing, though also a neuropsych can look at your adult experiences of difficulty in college and problems learning on the job skills. At least for me it became apparent just from my work history I had ADHD even before going through testing. Plus I suspect after you sit in the room with them for 7 hours of testing they ahem *notice* you aren't paying attention.