Dealt with this from an asshat running a semester-long school project. Solution: Drafting my own spec doc, sharing w/ rest of team, asking for comments, saying it would lock in two weeks.

Followed that doc for the next month or two.

Of course, the asshat was ticked off when the semester was about to close and tried to edit the doc (for the first time). I just said no.

I consider it a success even though even Those Kids who contribute nothing got As and I got a B+ despite working quite a bit.