Eh, well, recently re-identified as INFP, still feel slightly like a fraud posting in INFP threads. But I have an ADD experience to contribute, so here goes.
I was diagnosed with ADD in high school, when I was an overachiever in a demanding program requiring a heavy load of academics, extracurriculars, and volunteering, as well as having a weekend/holiday job. I struggled in high school, but I don't think it was really because I have an attention disorder. I think a more realistic perspective is that the program required a much-higher-than-normal level of focus.
My psychiatrist raised my Adderall dose quickly, despite my voiced concern, and one afternoon when I was in withdrawal from my morning dose, I had a psychotic break. I took myself off of it after that. I then realized I didn't need it during school, because school was structured, and that helped me focus. I ended up just taking it every once in a while after school or on the weekend when I had a huge workload staring at me. That worked really well.
I took a bottle of Adderall to college with me, but my crazy neighbor stole it a few weeks in, and I never renewed the prescription. I did better with balancing in college. I still did the Honors program but also did an easier major and didn't minor. I was involved in extracurriculars but still took time for relaxed fun. I did fairly well, only falling significantly behind in two classes, yielding a C and a D. One I forgot to do the online midterm for, and the other I slept through the final. (Lol!)
My conclusion for myself is that I do much better having a structured environment for focused work, which keeps me on task, and then being careful about not over committing myself outside of that. I do think that I will go to a psychiatrist again soon, and see if I can go back to having a bottle of PRN (take as needed) low-dose medication, for the days when I want to get my own projects done and struggle so much to implement them. I think those days are the real evidence I have an attention disorder.
But as for ADD/ADHD on the whole - I think it's real, but I also think, as is the general suspicion, that it's over diagnosed. There is pressure, at least in US culture, to overachieve, to be the best, the richest, the most powerful. There is praise for being extremely busy and for a neverending schedule. There is pressure on high schoolers to get into prestigious Ivy League colleges. The woman I work for calls one of her healthcare workers a "workhorse", as she is still working a 12-hour weekend day with that family while taking on a new full-time job where she is in charge of developing the program. Another girl I know was recently praised for working 84 hours (!!!) a week and never asking for time off. I recently talked to a friend of mine who lives in Japan, and she says that people in her community tend to work 10-12 hour days, 5-6 days a week. I have nothing against those who push, push, push themselves. I used to be that person - still am sometimes - and I understand that drive. But at the same time, people - kids especially - shouldn't be devalued if they're not living this kind of life. I think the truth is that many of us who have been diagnosed could do just fine living happy, healthy lower-key lives.