Sharing is an important part of the writing process. I have found that my students sometimes need help in making comments about their classmates writing so that it is both positive and helpful at the same time. There are also times when a writer might not have explained a part very clearly, and so students need to know how to ask a question for clarification without hurting the other student's feelings.
I copy these "star comments" on bright yellow paper and laminate them so they last all year (and beyond). The students use them when "peer revising" as well as in small writing groups when sharing final copies of stories, essays, poems, or reports.