This Dynamics Earth is a free resource from the USGS (United States Geological Survey) for educators on plate tectonics. It is a PDF booklet that you can download and it contains chapters on Developing the Theory, Plate Tectonics and People and more. There is also a website that goes along with it, This Dynamic Planet: A Teaching Companion that has information and classroom activities on plate tectonics.
The USGS also has some great resources on Volcanoes http://volcanoes.usgs.gov/about/edu/
These are excellent resources for teachers teaching plate tectonics and earth science.