This longitudinal study from Grades 1 to 4 investigated (a) the extent to which children select peers based on similarity in reading skills and (b) the extent to which children are influenced by the level of their peers' reading skills. The sample consisted of 1003 Finnish children in Grades 1-4, for whom reading fluency and comprehension were assessed. The same children were interviewed about their self-concept of reading ability at the end of kindergarten. The results of social network analysis showed that children had a tendency to choose new friends based on earlier similarity in reading fluency but not in reading comprehension. Furthermore, children became more similar to their friends in reading fluency and reading comprehension. Children with a high self-concept of reading ability and high reading fluency were particularly likely to be positively influenced by peers with high reading fluency.