Average person _where_?
If the school is bad enough, then an average student there (because there are many more students than teachers) might not be a good influence.
There are schools in my state with <50% graduation rate, the average student there won't even finish the school.
I am not saying anything about "worth of a person", I don't believe it is even a thing.
All I know that children (and many adults too) do similar thing that their peers do. So if I want to increase the chance that my child will graduate from high school, they should be around people who will graduate from high school. Similarly, if no one in their class will go to college, the chances they will go to college will be smaller.
Note there are exception to the each rule, and I am talking about "chances", not certainties.
So ability to graduate from high school determines the worth of a person?