Overall there are only small differences in boys' and girls' math performance; those differences depend on the age and skill level of the student, what type of math they are attempting and how big of a dissimilarity is needed to say that boys' and girls' math performance is truly different.
Gender differences are often larger among higher-performing students but not necessarily for lower- or average-performing ones. Within this specific group of higher-performing math students, boys tend to perform better.
A recent meta-analysis of research on the performance of students from elementary age through adulthood found boys tend to outperform girls in more complex areas of math such as those involving more advanced problem-solving. In contrast, there are no differences—and, in some cases, an advantage for girls—on more basic numerical skills and on math problems that have a set procedure for solving them.