This summer, Khan Academy‘s free, online educational resource is launching grade-specific math “missions” to help kids review the previous year’s lessons and get a jump on understanding concepts to be learned in the fall.  Categories:  Early Math, separate levels for Grades 3-8, Algebra I & II, Geometry, SAT Prep, Trigonometry, Probability and statistics, Pre-calculus, Differential calculus, Integral calculus, Multivariable calculus, Linear algebra, and Differental equations.