The US Forest Service has a very cool site called the Investi-gator, that is an upper elementary school science education journal. There are articles on leaves and why they change colors, ozone, soil activity, and much more, with discussion questions, interviews with scientists, lesson plans and assessments to use with students. You can download the journal issues, view them online, or order free copies for your classroom.
This is another great educational resource for teachers. http://www.scienceinvestigator.org/