How to anonymize submissions and ensure each student gets exactly one chance to submit? I am teaching a subject for a group of students I have not met before, and the exam coming up. It is a 14-day take-home exam. My previous experience with examining similar students indicates that there is a somewhat widespread problem of failing to answer in sufficient detail or sufficient rigor. (My subject is rather &quot;mathematical&quot;, but the students are rather &quot;not mathematical&quot;, so they are not used to mathematically rigorous thinking.) When reading their answers, I feel I would like to ask about the omitted details*, and I suspect quite many of the students would answer my additional questions correctly. If only I could provide them this chance...
I thought of allowing the students to submit their drafts early. Then I would glance over the answers and comment on those who should be expanded or detailed, without indicating whether the content of the current answer is correct or not. I think this would achieve the goal.
However, there is the problem of anonymity. Normally, the students submit their answers to an online system which anonymizes them and only then do I get to evaluate them. The system cannot be used for early draft submission, though. Another way would be for the students to send me e-mails with their drafts, but that would breach anonymity. Question: Could you recommend a solution of how to anonymize the draft submission? I also would like to ensure that each student is only given one chance to submit the draft (which seems like an additional difficulty in designing an anonymized system).
*You could suggest to formulate the questions absolutely precisely so that there is no way a thoughtful student would miss what the answer should be and how detailed it should be. I am trying this to an extent (taken to the extreme, it would make the questions awkward), but this does not always work as well as I would like. Also, what I am trying to evaluate is primarily not the mathematical rigor but the general understanding and some other things. As long as a student can answer correctly and in sufficient detail (regardless of whether this is right away or after additional questions/comments from me), I feel the student deserves a good grade.
In an online file sharing system (e.g. dropbox, google drive, onedrive...) create as many folders as you have students. Create a share link for each folder with write access.
Send the share links and the list of student emails to a trusted third party, and ask them to randomly assign a share link to each student.
Tell the student to upload (anonymously) their submission to the shared folder they were assigned to.
Upload your own feedback in the same folder.

It's a bit of a hassle but it works. There is a trusted third party involved, but you cannot get around that (just like for your exams proper, there is a trusted third party involved, namely, the online system).

Federico Poloni asks why a third party is strictly necessary. As this is a rather trivial question, I do not expect to be able to find a citation in the literature, but here is a mathematical proof. For simplicity, assume that there are two students, A and B. The instructor must give some information to A and B such that

the instructor can verify that no student submits the same work twice;
a student cannot impersonate another student to get around this restriction;
the instructor must be able to provide feedback regarding some submission and ensuring it arrives to the correct student.

Because of 2, the instructor must give some different piece of information to A and B to &quot;sign&quot; (in a cryptographical way, for example), their submission. A different key must provide a different signature because of 3, but the same key must always yield the same signature because of 1. Without a third party, the instructor must know what key is given to each student. It is then trivial to reuse that information to know what key yielded what signature, which can be use to breach anonymity.