Math/Science Nucleus is a non-profit in California that runs several museums and educational programs. They have a free, complete, online science curriculum for K-6. The Elementary curriculum is organized into six units of six weeks each. The cycle is repeated each year with increasing depth. Each unit comes with slide shows, story books, activities and instruction. The animation is very basic, but not hokey. The Secondary curriculum appears to be a work in progress. However, the Earth Science unit is complete and could serve as a complete middle school earth science curriculum. Kits of materials for activities are available for sale. Covers K-6 completely and earth science for middle school. Completely free.