StarChild's The Life Cycle of Stars (grades 3 - 12): Great resources for upper elementary, middle, and high school! Download an activity book that includes an explanation of stars as well as activity pages. One is available for younger students, and one is available for high school students. Posters and other resources are available here.
Star Light, Star Bright (middle/high school): Students can use four interactive modules to learn about star light and temperature. The modules are titled "Catch the Waves" (light is made up of colors); "Making Waves" (energy); "Heating Up" (wavelength, temperature, and color connection); and "Stellar Encounters" (identify star temperatures).