I don't think you can diagnose ADHD based on an IQ test. There are other inventories that the psych should be able to give you and some of them do computerized testing (although I'm not sure how accurate it is, since my ADHD dd scored in the average range on the computer testing).
working memory and processing speed (esp. working memory) tend to be lower in those w/ ADHD but not necessarily. My DD had slow processing speed but high working memory. In real life, she has poor working memory, for instance yesterday she had her instrument in her hand to go to band, then halfway there I realized she didn't bring it out the door. Scattered, disorganized...those are signs of poor working memory. WISC didn't pick that up and she's great at repeating strings of digits. Ask her to memorize names of capitals, though, and that's very hard for her. She is very slow in school because of how distracted she is. She'll be in the middle of a math problem and can't recall 9X7, so loses focus and starts looking around the room. Not everyone w/ ADHD has that trait though. She has a really hard time with distracting sights and sounds. If she tried to do math and someone near her was humming, whispering, or tapping their pencil, that would be the end of her.
