Boys are thought to be stronger and are treated more roughly and played with more actively than girls as early as birth. As children get older, girls are protected more and allowed less autonomy than boys, and girls are not expected to achieve as much in the areas of mathematics and careers as are boys.
Power and control are the real social motives behind the division of sex roles, through the division of labor. Not simply differential socialization, the assertion is that there is no motivation for men to relinquish any of their power and control to women (abortion issues, equal pay issues, child care issues). Confining sex role expectations can restrict personal and family development - don't forget we live in a society that expects women to work (Economy) and expects them to care for kids (Family) and expects them to develop