The issue that you are concerned about is called “functional impairment”.
The threshold is different depending on context.
For example, to qualify for special education in the United States, the functional impairment has to be very specific to education and very high.
However, for a clinical diagnosis, it just means that your symptoms prevented you from reaching your full potential.
I was in a similar situation.
However, you could see my symptoms and functional impairment, not necessarily in my grades, but in my injuries and trips to the emergency room, types of behaviors that got me disciplined the few times that I got in trouble, and social issues. You could also see it in the number of physical activities that I engaged in from sun-up to sun-down. I probably would have gotten in a lot more trouble if I wasn’t going from school, to musical rehearsal, to swim practice, to karate all in the same day!