The University of Washington has an excellent science education website,Tools for Ambitious Teaching, that discusses the theory of teaching science as well as some practical tips on teaching, assessing and enjoying science with students. I link first to the “Big Idea” page because it has been the hardest concept for me to grasp and the hardest for me to pull together for my students. But it is well worth working on, and improving because when it is done well, there is a beautiful synergy that propels everyone forward.