ADD and ADHD exist.
Those kids who go out and pull crazy shit with matches don't have ADD, they're just psychotics with shit parents. There is a significant difference between a poor upbringing and ADD. I see these people a lot (I deliver pizza over a wide area) and its easy to see why the parents will blame ADD, because their too prideful to admit they blew all the "Baby Bonus" on giant TVs. The parents don't interact with their kids, or even clean up because their too busy eating pizza and watching Foxtel on one of their four MASSIVE Plasma screen TVs. Then they turn around and say "I haven't gone to a doctor yet, but my son's got ADD, just like his brother". These people really piss me off, I have ADD, I got the diagnosis when I was 20, But I didn't stick my pets into a dryer etc... They can't be bothered paying to actually see the doc and get informed that its not ADD, its just their inability get their obese arse off the couch and provide the kid with some HARD discpline.
PS: The medical community haven't stated is part of the evolutionary cycle, but they've stopped treating it with same descriptors as Schizophrenia or Psychosis.
PPS: As for not focusing, theres an aspect to the disorder called "Hyperfocus" where the individual is able to attain a level of concerntration considered abnormal in comparison to a non-ADD/ADHD individual. The "Hunter Vs Farmer" theory is currently the only theory that deals with this aspect.
PPPS: AADD (Adult Attention Deficit Disorder) is similar to ADD but the symptoms are only recognizable later in life, post-adolscence I think.