This might be way out there and something that could be a long-term plan, but I figured it wouldn't hurt to bring it up. What about doing different themes for Classcraft? Right now it's very fantasy based, but what if for each class or each new year (especially for teachers who teacher multiple grade levels like I do) the teacher could pick a different theme for the year.
Example: My sixth graders get the fantasy theme this year with mages, healers, warriors, etc. But then, when they become 7th grade next year, to keep their interest up, it becomes a sci-fi theme with soldiers, doctors, and tech specialists (warriors, healers, mages). Then the next year it could be an Indiana Jones-esq theme, or a western theme, etc. The old themes would stay available, but when starting a new class, one of the set-up options would be to pick the theme of the game for the year.
You could announce what the new theme would be around Christmas or so, and then it could go live at the end of the school year so that teachers could prep their quests and powers over the summer months.
It would keep things fresh and interesting - mechanics would work identically, just the powers and look of the maps and such would change with each new theme.