yup. i know plenty of people on 6-7 figure incomes who never went further than school education.
my boss used to earn between 7 and 10K a week being a tradesman. he still has 4/5 houses and hundreds of thousands worth of cars (even after losing a lot of it in the recession)
they are very inteligent / brilliant / driven people not average... an average person would need a good education or a lot of luck to earn that much...
some people are brilliant (in one way or another) and either choose not to do well at school or cannot do well because their "genius" is not for learning it might be for sport or art..
if you are a genius / brilliant an education does not really matter, if you are average good grades do matter