Copyright © 2015 UKLA This study relates to the results obtained in the development of reading comprehension (RC) and self-concept as a reader in students who participated in Llegim en parella (Reading in pairs), a Catalan peer tutoring programme. The research combines a quasi-experimental design with the use of comparison groups and pre-tests/post-tests for both variables; a qualitative approach is adopted by analysing the interactions in order to detect influencing factors. Statistically significant results were obtained for all students in terms of RC but only for student tutors in relation to reading self-concept. The factors involved in the improvements identified in RC are: reading strategies, scaffolding in inferential and deep comprehension questions. Regarding self-concept, the tutor's own role, his involvement with their tutees' progress, reading aloud and the metacognitive reflection processes, are all factors that enable us to explain the improvement in the tutor's reading self-perception. The positive influence of peer tutoring on the development of reading competence through this programme is clearly evident.