Yep. ADHD and ADD are sets of behaviors that can be ascribed to many causes. I can attest to exhibiting ADHD behaviors myself when my work life and family life have me maxed out. Doesn't happen often, but it does happen. Fortunately for me though, I am normally able to find balance in my life that prevents me from exhibiting this behavior often.
As public educator of 16 years (have taught 4, 5, and 8th grades), every student that I've had that carried with him/her a label of ADD or ADHD had either 1) a very complicated and stressful home life, or 2) An underlying hurdle that made their education more difficult than the typical student. These hurdles might be some form of learning disability (so often expressive or receptive language difficulties) that made their learning especially difficult for him/her.
On the positive side of medicating, I've seen medication help, as a cast and crutches help a student with a broken leg recover. The medication, along with family counseling to address the underlying stressors, helps an ADD/ADHD student develop positive habits in and out of school to produce positive outcomes.
Unfortunately, more often as well, the medication is used to address only the symptoms long-term, without ever addressing the underlying causes.