In proof-based courses for math majors, I have started teaching the students to use . I usually assign one problem each week that needs to be done in . These problems are graded either “Acceptable” or “Incomplete,” and the students are allowed as many re-writes as needed to change an “Incomplete” to an “Acceptable.”
Up until now, I either had the students print these out or email me the .tex file for me to comment on. No longer. I am probably way behind on this one, but I found out that it is possible to annotate pdf files. Students send me the pdf file, I comment directly on it electronically, and I email it back. No paper involved.
So far, this system seems to be working well this semester. The only (minor) problem is that I need to grade from my home computer—it seems like it is really difficult to annotate in Linux.