Turns out I was a pretty classic case of ADD in school, though it wasn't caught. When I was in grade school, I was doing very well academically. I was in the Gifted program, all A's and B's, etc. I had two teachers recommend me for Advanced Placement in high school (AP English, Math) But as school went along, my homework started to go bad - I would forget to do it, lose the homework or forget to turn it in, or just plain not do it. Or procrastinate and do it in the last minute, which sometimes worked out, often did not. My excuse at the time was "I don't believe in homework, they should give us time to do it in class; most people don't do their jobs at home" (haha). Maybe if instead of giving excuses I just let myself be seen struggling with it, my ADHD would have been caught. But then, at the time I also believed I was being lazy - I didn't like homework, it was boring and a lot of work, so I wasn't doing it.
Procrastination is a common symptom of ADHD, because it actually helps a person focus on their work. The "Fight or Flight" response kicks in with the approaching time limit, which floods the brain with stimulants, enabling focus or hyper-focus. Thus the student who waits until the last minute to write an essay, then stays up all night doing it.
I went from all A's and B's to graduating with a 2.3 GPA (a C+ at best). AP English at my school was "Speech & Debate", and while I really liked the debates themselves, I *hated* having to have every argument researched in advance with the sources written down (which...I now know is very important, and love researching things). I just couldn't make myself do the boring research in the library. In the end I ended up skipping most of that class, hanging out in the computer lab instead (which was far more engaging to my brain). And I really liked Math, I did quite well until Algebra 2 - that textbook was basically repeating Algebra 1 exactly, but with one new concept every chapter (and again, I hated all the writing involved in showing my work). I found it so boring, I basically tuned out and stopped taking Math. Which I'm disappointed in, Math turned out to be very important in my career, and it's harder for me to learn that stuff at this age.