Maybe not 80%, but remember, 1/2 of the population has an IQ of less than 100. And about 16% are less than 85 IQ.
WRT our education system, how is a teacher supposed to teach a blended class, where out of 30 students on average, 5 are under 85 IQ and 5 are over 115, and the rest between 85 and 115. One is likely to be over 130 and one under 70.
This assuming a standard deviation of 15. Some IQ tests are 16, but close enough.
Personally, I think a lot of children labeled ADD or ADHD are just too smart and boring in class. So they don't pay attention and tend to try to talk to the others. BT, DT.