Which of the following is true about high-income babies?

The behavior gap between rich and poor children is now a well-known piece of social science. Entering kindergarten, high-income children not only know more words and can read better than poorer children but they also have longer attention spans, better-controlled tempers and more sensitivity to other children. All of which makes the comparisons between boys and girls in the same categories fairly striking: The gap in behavioral skills between young girls and boys is even bigger than the gap between rich and poor.
   The gap grows over the course of elementary school and feeds into academic gaps between the sexes. By eighth grade, 48 percent of girls receive a mix of A’s and B’s or better. Only 31 percent of boys do.
   And in an economy that rewards knowledge, the academic struggles of boys turn into economic struggles. Men’s wages are stagnating. Men are much more likely to be idle than they once were and much more likely to be idle than women.
   We reported last week that the United States had lost its once-enormous global lead in middle-class pay. The depressing trend has many causes, but the social struggles of men and boys are an important one. If the United States is going to build a better-functioning economy than the one we’ve had over the last 15 years, we’re going to have to solve our boy problems.
   Two of the leading theories involve single-parent families and schools. Girls who grow up with only one parent fare almost as well on average as girls with two parents. Boys don’t. But the trends seem too broad for family structure to be the only cause. That’s where schools come in.