Update: You can also find videos on iTunesU under the University of Arizona.
The year I first started teaching all sections of science at my grade level was the year that NASA sent Spirit and Opportunity to explore Mars. Students loved seeing the pictures and learning more about Mars and the other planets.
Sunday, NASA successfully landed another robot on Mars, the Phoenix. Like the previous Mars mission, NASA has developed a website that has a section specifically devoted to education. While not all of the education section deals specifically with the details of the mission, all of it is pertinent to educating students about space and Mars. This is a great resource for when you are planning your space unit and would like a place to differentiate student learning. Student will gravitate to the section and activities that most interest them, essentially differentiating themselves.
For you, there has even been a Twitter account set up for the Phoenix.