I can relate to a bit of each of your stories. For me, it was grade ten math – basic to boot. Over and over and over. I gave up on it after failing it for the second or third time (I honestly can’t recall how many times I took that frickin’ class). No, I can. Once in regular day class, failed, so I had to take it at night school. Failed it there, so I enrolled one last time in summer school to take it. You might not believe me, but all three times I was taught by a foreign teacher. First it was a thick accented Chinese man. The second was a thick accented East Indian man, and the third of them (the loveliest of them all), was a very thick accented Polish woman I loved to listen to but couldn’t get her to teach me parabolas to save my life. I had a friend who sat beside the side wall blackboard who had a running “days of hell” 5-sticks cross off calendar thingy going behind the big map. I ended up tuning out of the class half way and counting down with him every day instead (since I paid for it, I felt it was an extra bit of hell).
You might find this pathetic, or you might find this silly (I’m on the fence myself), but I never finished high school. I’m one credit short. It’s an elective, so I can technically take anything I want, but it kinda bugs me that that one class keeps eluding me and I would only get my diploma credit if I could redo that one class with an ADD-friendly teacher. I have five years of college under me and many years in the workforce, but I keep thinking about that one class and why I couldn’t grasp that basic level of geometry when every other level in the previous grades were easy enough for me. Other than that one class, I couldn’t care less about finishing my high school credits. It doesn’t eat away at me like that stoopid math class I keep failing. It’s the failure, not the accomplishment, I keep dwelling on so obsessively.
And don’t get me started on scientific calculators. I think they were pretty much designed by the wickedest person who ever lived just to torture me. 
Having said all of this, I have to say, I found college sciences (save for pulleys and the math calcs for them) brilliant and a real delight for me. They were creative and interesting, and I had the best science teacher ever to teach me chem as well as reflective physics. It’s because of her I love physics as much as I do (again, save for those blasted pulleys I hate so much). It’s like she taught me how to see molecules and objects moving at angles as I talk about them, write about them or do their calculations. She was the math teacher I needed but never got. 
I’m deeply sad and feel cheated about that. I told her so, too. She just smiled and told me to watch my back when I get into the real world because there was always some asshole behind me waiting to take my job after making me look bad since I don’t think my other people. I only half understood what she was saying then, but it’s lately I’m fully grasping what she said and why, to me of all her students.