Castle Learning - www.castlelearning.com
We use Castle Learning as a tool to practice math skills developed in the classroom. Here is what they have to say about themselves, "Castle Learning is a K-12 resource which provides core testing content using a variety of formats. Alignment to state and Common Core standards provides the necessary data analysis to assist administrators in meeting district objectives."
Khan Academy - www.khanacademy.org
We use Khan Academy to reinforce math concepts taught in the classroom, and as a way for students to extend their learning and move at a pace comfortable for them. Here is what they say: "The Khan Academy is an organization on a mission. We're a not-for-profit with the goal of changing education for the better by providing a free world-class education for anyone anywhere. All of the site's resources are available to anyone. It doesn't matter if you are a student, teacher, home-schooler, principal, adult returning to the classroom after 20 years, or a friendly alien just trying to get a leg up in earthly biology. The Khan Academy's materials and resources are available to you completely free of charge."