Hi Fantasy,
This is a tough call. It sounds like you have some really valuable collaborative projects.
I teach a large online class every semester (~250 students). I haven't actually attempted a group project like this, but I have thought about how it might work. Would it be possible to assign students in each group to different jobs (e.g., student A drafts the intro, student B drafts the method, and so on)? They could work in a shared document (e.g., Google Doc) to easily view/edit what other students wrote, but they could work asynchronously. Perhaps instead of having the groups come up with their own mission, you could just assign a mission, or give them a small number of options to vote on, or have them sign up for one of the missions that you choose. It's probably not quite as fun as getting to come up with their own research question, but it would cut down on the need for synchronous communication.
If you choose to do individual projects instead, would peer review be an option? I haven't tried this myself, but I've heard of different tools to facilitate student peer review. This probably isn't worthwhile if you don't have an easy-to-use tool built into your learning management system.
What about having students sign up individually to do just one of the projects (one-third sign up for project 1, one-third sign up for project 2, and so on)? Is there any value in that? They would miss out on the collaborative aspect of the project, and they wouldn't get to experience all study types, but at least the grading would be manageable.
Of course it's also completely OK if you just can't find a way to make this work for you and your students this time around. These are extraordinary times!
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Heather Kirkorian, Ph.D.
Laura M. Secord Chair in Early Childhood Development
Associate Professor | Human Development & Family Studies
School of Human Ecology | University of Wisconsin-Madison
4105 Nancy Nicholas Hall | 1300 Linden Drive
Madison, WI 53706
kirkorian@wisc.edu | 608-263-4020
https://sites.google.com/site/kirkorianlab/------------------------------