I was one of those kids really good at math as a little kid, so people kept bragging about me being good, expecting me to be good, and pushing me into the academic level of math classes (alternative being applied).
Except there was an issue with this that no one ever noticed, I was only good at it because it was a lot of quick and simple repetition. Stuff people with Autism are recorded at excelling at... So I definitely had an edge in that department.
So when I entered the more complex math (Grade 10-11) where it required a lot more steps, varying approaches, explanations etc. That's when my grades started slipping, and suddenly I became one of the children struggling in math.
That being said though, according to my Math Teacher in high school (by chance I got the same one every year) part of the problem was ever since Grade 9 I did actually get most of the answers correct, but the issue was I simply jumping straight to the answer/result, and wasn't explaining or showing my process most of the time. And most of the time that I did manage to show my process I was using the wrong one, which meant I wasn't practising the skills I needed for the later years.
Now with it being four years after leaving high school (and five after taking math) I can pull open something like D&D and crunch the numbers insanely well.
But if you want me to handle most of the Math Tactics shown in High School? Good luck, I basically forgot that stuff the second Grade 12 came around.