"Harvard Education Letter" is published bimonthly at the Harvard Graduate School of Education. This issue of "Harvard Education Letter" contains the following articles: (1) The Greening of Environmental Ed: Teachers Focus on Complexity, Evidence, and Letting Students Draw Their Own Conclusions (Lucy Hood); (2) Like Teacher, Like Student: Online PD Helps Teachers Learn to Collaborate so Their Students Will, Too (Dave Saltman); and (3) The Virtues of Experience: There Is "No Magic" in Replacing Principals of Underperforming Schools.