The benefits of students learning together in peer-assisted learning (PAL) programmes have been widely reported. Implementing and evaluating PAL programmes provide specific challenges for academic staff. This paper explains how action research was used to design, trial and refine a same-year PAL programme to enhance student engagement. The PAL programme was successfully integrated into a multidisciplinary radiologic biology unit of study in 2010, following improvement over two trials in 2008 and 2009. The paper demonstrates the value of action research for designing the PAL programme to increase student engagement and for bringing research and practice together by using this experience to contribute to the scholarship of teaching and learning. Key factors influencing the success of the programme were: group size; the provision of structured and unstructured student support; peer assessment; the introduction of case-based learning; and the use of interactive tutorials. Achieving the appropriate balance of these factors increased students' engagement in their learning.