Tell them they can do just as well as boys in science and math because they can. Without meaning to, we may put limits on what our daughters think they can achieve. Your mother never liked math either. I know you can do well in math. And it's an important subject.
Insist girls take science and math courses every year.
Make sure you know which math and science classes count toward college or technical school requirements. Explain that without these courses, a girl may limit her future. Girls who do not plan to work outside the home may want or need to later. Math keeps doors open. Find out what math and science classes are like in your girl's school.