The closer the relationship is to 1, the better the prediction. This is a fairly high relationship which means that if you have a high high school GPA, the odds are your college GPA will also be high. The relationship between sex and quantitative skills is about .1, as is the relationship between sex and verbal skills. The reality is that girls as a group and boys as a group are more alike than they are different. And averages can be very deceiving.
Some boys are bad at math and so are some girls.
The overlap is much larger than the difference. Overall, sex differences tend to be smaller than most other demographic differences. Girls are much less apt than equally talented boys to go into math-related careers including engineering and the physical sciences. There is a biological basis for sex differences in math. Hormones cause everything.