Exactly. Education is the key. I don't think anybody would accuse women as being "less intelligent" than men. They simply just don't pursue college degrees in Math/Science/Engineering like men do. In fact, women's participation in these fields is going down over time.
So really what txtebow is implying is that white men are much smarter than everybody else, including white women. Therefore, you could conclude that having children with women would be constantly making the population dumber.
That, simply by virtue of gender your child would be more, or less, intelligent. Which is preposterous.
Put everyone in the same good schools, with positive family environments, and role models who push them towards STEM fields. Then feed pop-culture of being "smart" like in China and India, and you would be surprised how much "smarter" US children OF ALL RACES would appear.