Executive functions (the skills affected by ADHD) are the biggest predictor of academic and life "success". Without executive function, intelligence is largely irrelevant.
I recommend neuropsychology as part of diagnosis. I learned my son's "laziness" was actually an astoundingly slow processing speed. I have ADHD diagnosis myself and I learned my tested skills are not nearly so low as expected which indicated that environmental changes may offset my impairments - and they did. Neuropsychology may indicate the severity of symptoms, but cannot point the reason for the symptoms. ADHD is not the only cause of poor executive function and childhood sleep disorders are a common cause of "ADHD".
My nephew appeared to have ADHD. After neuropsych, now my sister knows he is neurotypical or gifted (she declined to be told IQ results) and his "symptoms" are counterwill. My niece in the same family presented with a severe academic delay - but she has ADHD most likely cause by high blood lead level.
I do not believe ADHD self-diagnosis can be done, there are too many differential diagnosis. ADHD is a diagnosis of elimination.
Diagnosis can be a lengthy or daunting process but I believe it's worth it. My DS9 is incompetent and cannot perform basic life skills without medication. Without medication he cannot function in any school setting regardless of the accomodations. Our home life was in turmoil and I was seriously considering putting him in foster care since he wasn't old enough for inpatient behavioral treatment. With medication, he is far beyond expectations for academics, hobbies, responsibility, and life skills. Putting him a first medication (which didn't work very well) corresponded with a 3-grade acceleration, and finding a best-fit medication corresponded with and additional 2-grade acceleration. When he was given school work at his intellectual level, his resistant school related behaviors disappeared and within a couple months his lingering behavior problems resolved. His anxiety and aggression/frustration disappeared.
