Time for Plan B.
Luckily, I had wavered between using that map, and the Water Challenge map (which is in 1.7.10). I set it up, and we were off!
I required all students to do the farming tutorial at the beginning, which was beneficial because it really showed off who was reading instructions, and who was simply trying to bash their way through as quickly as possible.
Once most students were through the tutorial, I made sure they were all in their individual sections (by colour) and explained that the objective was to survive as a group.
This particular world has only one water source, and very limited food resources (note to self: turn off animal spawning next time around) Students are expected to use the knowledge they gained in the farming tutorial to grow enough wheat to sustain themselves. Within the first 15 minutes, nearly all of them had died of starvation at least once. I froze the group, and we had a quick debrief about what needed to happen in order to ensure that all members of their group survived (for example, we determined that searching for diamonds was not strictly necessary...) We created slightly larger groups, I reset the world, and they tried again. This time, they chose specific roles aimed at providing enough food for all 5 members of their group, and most of them survived for the 20 minutes or so that they were logged on.
What I learned from this experience:
1. Always have a Plan B!
2. When students are in teams, arrange it so that they are also sitting near one another. I wanted to ensure a good mixture of students the first time around, so I assigned their groups starting at one end of the row and alternating between the three colours. The second time, when we regrouped, I assigned the colours in chunks so that students could communicate more effectively with the other members of their groups.
3. It's alright to reset the world in the middle of a session in order to redirect the activity and refocus the students on their objective.
My computer was struggling yesterday, so I wasn't able to grab video of our time in the world, which was alright as students were divided into three separate, fairly large areas so it would have been difficult to capture much of visual interest. Next time, I will set up teacher-only teleport stations so that I can quickly move between the areas.