First, start with our printables page, where you'll find lots of worksheets organized by topic. Take a look at Eighth-Grade Math, Science, Language Arts and Social Studies (scroll down to find eighth grade).
Try our quiz: What Your Eighth-Grader Should Know
Be sure to visit our homeschool page, where you'll find great articles and other free resources on homeschooling.
Also, we have Subject Toolkits for Homeschoolers in reading, math, and history!