If you haven't been to the NASA Educators web site, it is well worth a visit. This site is loaded with all kinds of helpful information. I just downloaded a 95 page packet on Optics that includes 14 different activities for kids in grades K-4, 5-8, and 9-12. And there's well over 100 publications available! Scroll down to where it says Find Teaching Materials to search or browse.
Besides the teaching guides, they have feature articles, images, podcasts, eClips (videos), student material, NASA's Kids Club online games, and other educational opportunities. You can register for a free MyNASA account to organize your personal resources on the very extensive site.
During one visit to the site, it had a box that linked to the Digital Learning Network (I have not seen the box again since.) On this site NASA offers free live web casts and, if you have the equipment, classroom video-conferences. It looks like you just click on the link when the webcast begins; right now it brings you to an empty chat room for that webcast. I'm interested to see one, the next one being March 10.