Khan Academy is a great FREE resource.  Students and parents can sign up for accounts and gain access to instructional videos, practice problems and quizzes.  Participants are provided with instant feedback on the work they complete.  This is a great resource to consider if your child is struggling with any of the skills on their grade level check-list.

All students in grades K-8 have i-Ready Classroom Mathematics as their core curricular resource. There are helpful documents, videos, FAQ documents and even math discussion activities that you can do with your children at home.

Students in the courses Algebra 1, Geometry and Algebra 2 are using the eMath Instruction curriculum.  This link will bring you to the main page and you can navigate to your child's course and see all units, lessons and HW for the course.  As long as you ask your child's teacher which unit and lesson they are on, you should be able to access the materials from home.