In addition to Michelle’s great suggestion, does the version history button help you at all? I’m not sure what unit you’re in, but I’ve often used that to see my students’ progress in several of the units. It’s not a perfect solution to your need, but it does help follow their progress.
I’ve had students tell me in the past that they suddenly ‘lost all their work’ when in fact they actually just hadn’t finished (oops) and this is one of those tools that has made it easy for me to have that heart-to-heart with them about what’s going on and why they didn’t finish something (web pages would be a good example).
Just thought I’d mention in case it helps!