This figure, derived from the National Council on Economic Education's What American Teens & Adults Know About Economics survey, shows the relationship between how interesting people think economics is and how much they know about it. Notice that the rank order matches up neatly: Male adults know the most about economics and are the most interested in it, followed by female adults, male high school students, and female high school students.
The simplest explanation is that men know more about economicsbecause they find economics more interesting than women do. Admittedly, I've got no proof of causation. But as far as I know, this is the strongest evidence that the simplest explanation is viable.