In many English classes, students read each other's essays and write comments. Does this help? Researchers looked at 26 studies, and the answer was yes. It helped students write their ideas better, but it helped grammar less.

In one study, some students only gave comments, and others only got comments. The students who gave comments improved their own writing more. Reading a friend's essay carefully can teach you how to write.

Peer feedback means that students read and comment on each other's writing. A meta-analysis of 26 studies in second language writing found that it had a clearly positive effect. Its effect was larger for content than for vocabulary and grammar, and it grew when students had more time to write and when the program lasted longer. One study compared two groups of 91 students.

The "givers" reviewed other people's essays but never received feedback, while the "receivers" received feedback but never reviewed. By the end of the semester, the givers had improved their own writing more, and lower-level givers gained the most. Reading as a reader seems to help students notice problems in their own work. However, peers are less useful for correcting grammar.

Many teachers ask students to exchange drafts and comment on each other's writing, yet learners often doubt whether classmates can really help. Research suggests they can. A meta-analysis of 26 second language writing studies reported a clearly positive overall effect. It found no significant difference between peer feedback, teacher feedback and self-revision, although the authors called this tentative because few studies made such comparisons.

The effect was larger for content than for vocabulary and grammar, and larger for revised drafts than for new compositions. Perhaps the most surprising evidence comes from a study of 91 students. Givers reviewed anonymous essays without receiving feedback, while receivers used feedback without reviewing. Over a semester, the givers improved their own writing more, and lower-proficiency givers benefited most.

A plausible explanation is that evaluating someone else's text trains the reader's eye that writers need when revising. There are limitations, however. The two groups received different instruction, peers often miss grammatical errors, and untrained reviewers tend to focus on surface mistakes. Training students to comment on ideas and organization appears to make peer feedback more valuable.