User Reference Material
Khan Academy is an educational organization with the goal of creating a set of online tools that help educate students. Khan Academy is on a mission to provide a free, world-class education for anyone, anywhere. Their interactive practice problems, articles, and videos help students succeed in math, biology, chemistry, physics, history, economics, finance, grammar, and many other topics. It provides teachers with data on how their students are doing so they can identify gaps in learning and provide tailored instruction.
Khan Academy is backed by research.