I use this for more creative projects to get students thinking about what makes a good piece of work and to reflect on the work they have done. It is also a great way to reduce the amount of marking and students seem to care so much more about what their peers think.
Firstly get the students to wonder around and look at all the work, putting positive general comments in the big box. After a while I then play some music and when it stops they have to sit at the nearest piece of work and mark it. It helps to have a mark scheme up on the board for them to refer to and to give some suggestions of possible targets. After the official peer assessor has made their comment and given a target and an attitude grade, it is down to the author of the work to reflect on the comments and what they would do to make it better. I like to give a chance for appeals about grades, which can be quickly dealt with by a quiet conversation.
I usually add my own comment, target and grade at the bottom, but this is made quicker by the students already giving you comments and targets to base them on. If it is a group piece of work, it works well to photocopy the sheet so all can stick it in their book.