Chess has a similar problem. Girls may show promise in chess, but when they see that chess club is 3/4 male, or more, they tend to drop out, especially at older ages.
The local chess club is more than 80% male and almost 90% Asian, although there are more whites than Asians in the schools. It may well be that children prefer to associate with their own sex (at least before puberty) and race and choose activities accordingly. The same mechanism may partially explain similarly skewed demographics of school math teams. I don't see what can be done to make participation more representative. You can't turn away interested children, and the level of interest appears to vary by demographic group.
