The flipped learning approach has been growing in popularity in both higher education and K-12, especially for its potential to increase active learning and student engagement. However, further research is needed to understand exactly how the flipped approach enhances student engagement. This narrative systematic review synthesises literature published between 2012-2018, focused on the flipped learning approach in K-12 contexts, and indexed in 7 international databases. 107 articles, book chapters, dissertations, conference papers and grey literature were included for review, and the results are discussed against a bioecological model of student engagement. Studies in this review found the approach to overwhelmingly support student engagement, with 93% of studies citing at least one dimension of behavioural, affective or cognitive engagement, whereas 50% of studies reported facets of disengagement. Collaborative technologies such as Google Docs, Google Classroom and Edmodo were particularly linked to engagement, with videos not created by teachers more likely to lead to disengagement. The results indicate that the majority of research has been undertaken in North American and Asian high schools, heavily focused on student perceptions of flipped learning and achievement within STEM subjects, especially Mathematics, with a slight preference for quantitative methods. Only 12% included a definition of student engagement, and less than half used a theoretical framework. Future empirical research should ensure that all contextual information is included, including year level of student participants, that multiple methods of both quantitative and qualitative data collection are included, and close attention is paid to grounding research in theory. Further research is needed on parent, teacher and school leader perceptions, as well as longitudinal and multiple-class studies.