A systematic literature review of international empirical research was conducted to understand the impact of primary-secondary transition on children's experiences, outcomes and protective/ risk factors. The review covered the period 2008-2018 and met the gap in previous literature reviews. Using the EPPI-Centre approach, authors included 96 studies in the review. Synthesis of the findings suggested that, in the main, perceived and real relationships with teachers and peers led to positive or negative experiences. Pupils and parents were primarily concerned with changes in relationships during the transition from primary to secondary school. Some studies reported that transition can also have a positive effect on opportunities for establishing new friendships. There was a decline in educational and wellbeing outcomes, and there was a link between the two. However, we cannot say with any confidence whether this impact on outcomes was as a result of the transition to secondary school, and whether it was sustained over time. Protective and risk factors were related to the child and significant others in their ecosystem. There were contradictory findings about the impact of organisational and educational systems. A limited number of studies examined the differential impact of transitions on children with additional support needs. This review is the first to bring together various aspects of transitions and as a result provides some unique insights and makes an original contribution. It became clear that it is difficult to predict the impact of interactions between experiences, outcomes and factors, given the gaps in existing literature. The paper concludes with recommendations for policy, practice and future research.