The Sieman's We Can Change The World Challenge is a fantastic contest for grades K-8 where small groups of students identify an environmental problem in their own classroom, school or community, work to find a solution and then share it with the world. The site has so many wonderful resources (videos, lesson plans, eBooks and more) that even if you decide not to join the challenge, you'll still find many of the resources extremely useful in your science classrooms. I particularly like the virtual labs.
Here I take about 8 minutes to give you a tour of the Sieman's We Can Change The World Challenge. Here's to us all becoming "Agents of Change!"