Most schools (maybe I am wrong) do not practice thinking skills but our ability to memorize. Example:

1. Biology = Memorize Latin names and human organs
2. Physics = Memorizing natural law theory and scientist formulas
3. Maths = Memorizing calculus formulas and other dimensional calculations
4. Geography = Memorize facts about the earth
5. History = ... (obviously) Perhaps the above

examples are not entirely correct, there are some cases that require the ability to think like solving the case of mathematics and physics (using logic), but almost most of what is learned in school / college is rote.

Few subjects actually teach us about thinking. Some areas that "I think" actually train the ability to think logic / reason that is:
Coding / Programming
Engineering / Engineering
Communication / Language
Art / Design.

Now let's learn why those who are mediocre in school even DO can succeed in his life. Of course not everyone who is mediocre / DO is successful, so are those who succeed in school not all succeed / fail in life, what we need to learn is how can those people succeed even though they do not have any diploma or achievement in school.

To be successful as Bill Gates / Mark Zuckerberg we need to learn the process (not the DO), there is a similar pattern from those who succeed without having any diploma or achievement in school that they build assets as early as possible and create something from the asset .