One of the things that separates Minecraft from similar sandbox-style games (such as Second Life) is the ability to host server installations. This allows teachers to restrict participation to the school community and control permissions. In addition, this also allows teachers to customize game servers with plugins. These community built modifications allow administrators to set up towns, in-game economies, and even teach programming.
Having control over a school server has other advantages. Outside of school hours can be established and game play can be restricted to those times. Moderators can be chosen or elected from the student body, or from alumni. Curriculum such as needs and wants, elections, community interdependence, the importance of laws, and introductory programming can all be addressed in a way that engages the learner and encourages independent exploration.
I really don't know what this would look like but I am excited about the possibilities. I hope to experiment with the idea in an after school club and see where it goes. Because Minecraft has an open-world approach, the possibilities are exciting. Just check out the video below of the Minecraft built 16-bit computer - Crazy. I'll keep you posted.