Well, I learned from my psychologist that ADHD directly affects testing and test anxiety, which I suspected, but I also learned that those who have ADHD who are also intelligent, can actually brute force their way through school, but when they hit college, they hit a wall and they tend to fail.
ADHD also can directly affect IQ testing by as much as 20 points, due to the attention problems the disorder causes.
I directly had that experience, because that describes my entire school career. Did fine through elementary, middle, and did kinda okay in high school, but I got put on academic probation twice in college because of me just raw dogging academics with pure logic, no studying, and untreated ADHD.
Seriously, if you're young and suspect you're going through something please, for the love of all that's holy, get it addressed while you're still young, as untreated issues only get worse as you get older.
I wish I had this knowledge at least 10 years ago, and I wish I had addressed this when I was a child.