This paper reports on an ongoing programme to develop new academic journal reviewers through mentoring. It analyses data from correspondence between experienced reviewer/mentors and new reviewer/mentees at an online journal. With the overlying objective of improving internal review quality, the mentoring programme has been initiated to raise awareness of review issues, instead of formally evaluating reviewer performance. It stresses the importance of recognising the diversity of norms in academic writing, which builds on studies into the editorial process of online journals. Findings show the mentoring process is yielding benefits in sensitising new reviewers how to give constructive feedback to authors, argued in this study as "brokering" knowledge of reviewing practice. Additionally, reviewer/mentors report that they too have become more aware of how to communicate effectively with new reviewers.