So I'm quite confused by this article's emphasis on boys outperforming girls more in richer school districts. If you look at the scatter plot, girls outperform boys in English by a much larger margin.
The fact that girls outperform boys academically is relatively well known. The article is about the (lesser known) fact that the math gender gap is correlated to the socio-economic status of the district, while the English gender gap is not. Which isn't to say the overall gender gap isn't important or interesting, it's just not what the article's about.