Hippocampus is a fabulous site for parents, homeschoolers, tutors or even teachers to use as a resource for students in an array of high school and beginning college level classes. The site offers step-by-step tutorials for concepts in algebra, geometry, precalculus and calculus, as well as several high school level science classes, psychology, US government and US history. You can follow the normal course of the curriculum in each class, or select a problem area to get a clear explanation and practice problems.
More at: http://www.hippocampus.org/
Visit GLF's myHippo page: http://www.hippocampus.org/myHippo/?user=myGLF