Writing is one of the four skills of language which helps in releasing strong emotions, clarifying information, stimulating memory and demonstrating mastery of content. One of the ways through which students do master writing content is peer interaction. Despite the importance of writing, employers still complain that school leavers do not know how to write, implying that either they were not taught writing or that the classroom environment, of which peer interaction is part, was not adequate enough to prepare learners for the kind of writing that they will do after school. In this paper, we explored the influence of peer interaction on writing mastery. Using interviews, focus group discussions and observation, we collected data from three secondary schools in Uganda. Our findings portrayed that peer interaction supports the mastery of different processes of writing; however, there was little interaction in class because some of the teachers and students were against it for various reasons. Therefore, there is a need for teachers and students to be trained on how to maximise the benefits of peer interaction to enable students' mastery of writing.