As a parent, I purchased a license to IXL Math for my 3rd grader to help with his math skills. I was surprised by the wide variety of practice skills available. Over 200 for third grade alone. IXL Math has practice skills for Pre-K through 8th grade, covering everything from basic math to consumer math to geometry and linear functions. Repetition is a great way to learn math skills and IXL provides a good environment for your child to practice a skill repeatedly if needed. You can visit the site and preview the question categories.
The site advertises that they will provide content for grades 9-12 soon. The cost for one license per year is $79. With the wide variety of skills available for us to practice, it is a tool that I plan on using at home with my kids for the foreseeable future.