Recently I was checking the links & adding some new ones on my page about math help and tutoring.
Here are some that are the "cream of the crop" when it comes to math help message boards. Typically, they require a student to show some work before someone helps -- or the helpers will only point out how to get started. You could definitely use these message boards as a parent if you can't figure out a problem in your child's math book, or if you have generic math or math education questions.
Ask Dr. Math
Browse old math questions or ask your own. Expert answers. The archives have thousands of answered questions covering all math topics from elementary to college level.
S.O.S. Mathematics CyberBoard
Active discussion board where you can ask math questions about algebra, calculus, geometry, trigonometry, probability, college math, computer science, physics, and more.
Mrs. Glosser's Math Goodies Forums
For students, teachers & parents. Homework help, Teacher Talk, Parents place.
Math Help Boards
From pre-algebra on through university-level math. It has experienced staff, is completely free, and as a policy does not give answers away without the asker showing some effort.
A math homework help forum.