Sex differences in intelligence means differences between males and females in mental abilities such as problem-solving and thinking. Some people say that boys are better at some kinds of thinking and some people say girls are better at other kinds of thinking. But we actually don't know for sure if there are any real differences between boys and girls in intelligence. Scientists have done lots of tests, but even though some researchers have found some small differences, most researchers say that these differences are too small to really make a difference. So, it's best to treat boys and girls the same when it comes to intelligence!