I know that I agree with this statement, and have for a very long time, mainly because of my father. My father was not your traditional student -- he was very smart, but didn't do well in school. He went to some college, and then joined the Air Force working on the electronic systems on fighter jets. After that he started working in the beverage industry.
Now a lot of people would look at his history and simply write him off, and in some ways I did too. For the most part when I had questions about school work, I would go to my mom for help. But then I started to get into subjects that my mother couldn't help me with, especially physics, and to my amazement, my father stepped in and was phenomenal. He knew the formulas I needed to work with off the top of his head and could explain things to me in a way that made sense. And when it came time to work with circuits, he was a whiz.
Looking back I should have realized that he was going to be a big help because that was his thing, even if he didn't do that for years. He was responsible for the electronics on the airplane that ran the bombing equipment, so of course he needed to know simple Physics 1 circuitry, heck, he could have probably been really helpful to the AP classes.
I guess my point is this, don't write anybody off because they might surprise you.