Click on Participants in the sidebar. Scroll down to the list of all your students and find the student's name that you would like to log in as. Next, to their name you will find an option to Login as.
You will now view Peergrade exactly as your student. To get back to your teacher account, click Stop Impersonation in the bottom right corner of the screen.
Note: Actions taken while impersonating students will affect their student account.