He was wrong.
Hyde performed a huge meta-analysis of studies measuring math and science by gender across different grades and levels.
Despite all the negative messages girls and women hear about math and science, there was no statistical difference between how well girls and boys performed in these subjects. In fact, the huge performance gap came not between boys and girls, but between American students and international students. American students score consistently lower than their Taiwanese and Japanese peers.
Yet, despite a mountain of evidence to the contrary, we continue to believe that boys are better at math and science, and that girls are better at verbal skills. Hyde found that women and men are actually more alike than different. She calls this idea the "Gender Similarities Hypothesis".
So, if there's no difference in ability, why do women continue to underachieve compared to men in some fields (women actually earn more graduate degrees than men in some areas, such as biology, but less than men in others, such as physics)?
Because we continue to believe the gender stereotypes. In Hyde's words, "Overinflated claims of gender differences carry substantial costs in areas such as the workplace and relationships."
I wonder how our world would change if we believed that women and men could succeed equally in any field.