My so-far limited formal education(I'm a senior in high school) itself has taught me some things about biology and chemistry and medicine that I might not have learned purely of my own motivation, but in the case of chemistry, I learned most of that by reading the textbook and then doing other things in class and ignoring the teacher. In the case of my biology class, I wasn't motivated enough to read the textbook(or to take it to class or home, for that matter), so I took notes and did other things in class and learned it. In the case of anatomy and physiology(the source of aforementioned medical knowledge), we don't have textbooks, so as in biology, I take the notes and otherwise don't pay attention in class but still learn it.

Calculus is something I did not from my formal education; however, I was taking the course when I learned it. I had wanted to learn it for a while(my first attempt was at around 8 years old, but I saw the strange notation and didn't realize the text explained it), but I had yet to actually do so. In part, this was because I didn't have any books on the subject and the wikipedia article didn't seem like a very good introduction. When I received my textbook for the course, I learned differential calculus. After a while, I got bored and learned integral calculus. I got bored again and learned how to do iterated integrals and partial differentiation. I'm glad I got bored so often during that year because the course itself only got us through definite integrals.

In American secondary education, I think that the main educational utility is from the provision of textbooks to the students. That has been, at least, the main utility of my school to me(other than exposure to such things as the creative writing and theatre clubs). My school is, however, a particularly bad public school in a very poor small rural town. It's possible that other formal education may be much better(I certainly hope that the college I attend next fall will utterly change my mind about formal education).

I suspect there is the pattern: very limited knowledge obtained during formal education, most as self education.

Help those self-educating?

I know, the path is a little beaten by, for example, certification programs.

Is there business opportunity? Maybe.