Peergrade automatically allocates reviewers to submissions. We try to do this as intelligently as possible to ensure that all submissions receive feedback of the same quality.
The reviewers are not allocated to submissions before the feedback period opens - instead they are allocated "live" while the review period is taking place. This means that Peergrade only decides which submission a reviewer should give feedback to, just at the time when they are about to start that review.
Imagine that there are 3 students: Alice, Bob and Charlie. Each of them submit their work alone, and we want each student to review 1 submission.
Initially, no reviews are allocated. The first thing that happens is that Alice goes to Peergrade to give a review. In this case, she can be allocated to either Bob or Charlie's submission (not to herself), and since they both have no reviews, she will just get a random one of them (let's assume Charlie).
Now Bob goes to Peergrade to give a review. Charlie has already been allocated one review, and Alice has not been allocated any reviews yet. So Bob is allocated to review the work of Alice.
Finally Charlie goes to review something. Alice has already been allocated a review, so Charlie is allocated to Bob's submission (since he has no reviews).
Now everyone has given their reviews (and all submission has received a review), and the session is over.