Temple University currently hosts two Minecraft servers for educators.
Dig is a Bukkit server which has been used for joint projects between Christopher Reeves (a teacher at Prospect Mountain High School in Alton, New Hampshire), Catherine Schifter (professor, Temple University College of Education), Matt Palladinetti, and Rick Moffat (both from Temple University Computer Services). Randall Fujimoto has also hosted community programs about World War II Japanese internment camps on Dig.
We also hosted an after school Minecraft club for The Meredith School, a middle school in the School District of Philadelphia, in the spring of 2013, and we hope to return to Meredith in the fall to help them use Minecraft as a tool for delivering math curriculum.
Our second Minecraft server is running MinecraftEdu, a mod developed by TeacherGaming. MinecraftEdu has a number of features and enhancements which make it easier for teachers to manage a classroom of students, in addition to creating and sharing MinecraftEdu lessons.
Our MinecraftEdu server is open to the Minecraft Teachers Google group, as well as any educator, anywhere in the world, who wants to experiment with MinecraftEdu and network with other educators exploring Minecraft. Join the group, introduce yourself, and ask about joining our MinecraftEdu server. You do need a MinecraftEdu license, available from the MinecraftEdu website. The Minecraft Teachers Google group linked above is a great place to ask questions about Minecraft and MinecraftEdu.