We document and analyze the emergence of a substantial gender gap in mathematics in the early years of schooling using a large, recent, and nationally representative panel of US children. There are no mean differences between boys and girls upon entry to school, but girls lose more than two-tenths of a standard deviation relative to boys over the first six years of school. The ground lost by girls relative to boys is roughly half as large as the black-white test score gap that appears over these same ages. We document the presence of this gender math gap across every strata of society.

We explore a wide range of possible explanations in the data, including less investment by girls in math, low parental expectations, and biased tests, but find little support for these theories.

Moving to cross-country comparisons, we find earlier results linking the gender gap in math to measures of gender equality are sensitive to the inclusion of Muslim countries, where, in spite of women’s low status, there is little or no gender gap in math.

A new paper from Roland Fryer and Steve Levitt.