Explore the solar system with text, pictures, sounds, and occasional movies at The Nine Planets. Each of the planets and major moons in the solar system is described and illustrated with pictures from NASA.
If you don't have any time to look at any other links, then this is the place for you. Windows on the Universe offers the choice of appropriate educational levels — beginner, intermediate, or advanced. It is brought to you by the National Earth Science Teachers Association.
For K-3 educators, Ready Jet Go! from PBS has short videos and resources for teaching about the solar system and the planets.
This lesson for grades 3-5 combines number sense and data analysis with planetary science, as students explore ways to order the planets.
The European Space Agency offers Teach With Space: Our Solar System, a complete teacher's guide to a research project for grades 3-5.
Want a convenient way to find NASA space science resources for use in classrooms, science museums, planetariums, and other settings? Check out the NASA Wavelength. It's searchable or browsable by keyword, topic, and/or grade level.