While in elementary and middle school, the math skills children need to know are organized by grade level, in high school they are grouped by concepts — such as algebra, functions, geometry ...

For high school students, math skills and understandings are organized not by grade level but by concept. Students will advance their understanding of functions as relationships between inputs ...

Khan Academy offers free math classes in grades PK-12, as well as college-level courses. Cuemath offers live online math classes. Parents.com’s “new math” explainer offers video and visuals.