Stephen Machin and Tuomas Pekkarinen:

Do boys and girls differ in their intel- lectual and cognitive abilities and, if so, in what way? These questions have raised considerable debate, both in terms of average performance and in terms of variability around the average.
Empirical research on gen- der differences in achievements produces mixed conclusions, with some evidence that favors boys and some that favors girls (1–4). In many countries, girls show superior performance in school examinations, which is also reflected in higher rates of attendance in tertiary educa- tion. In addition, girls have been improving their position rela- tive to boys (5, 6). In countries with a more gender-equal cul- ture, the gender gap that is usu- ally in favor of boys in average mathematics test scores is erased or even reversed in favor of girls (7).