This report was commissioned by The Centre for Transforming Access and Student Outcomes in Higher Education (TASO) to address gaps in our knowledge about the barriers to students from widening participation (WP) backgrounds accessing, and succeeding on, sandwich year courses. Sandwich courses are defined as undergraduate degree programmes that include a year-long placement in industry or part-time work-experience alongside a degree-course. Existing research has demonstrated that considerable advantages follow from taking a sandwich course, particularly in relation to accessing professional-level employment on graduation, and that these advantages are often heightened for those from WP backgrounds. Nevertheless, it is also known that students from WP backgrounds are much less likely to take up the opportunity of a sandwich year. Although there has been some limited research on the reasons for this, such studies have often focussed on a single higher education provider (HEP), or a single degree subject. In addition, while some of these studies have made recommendations about how the problems they identify can be addressed, in no cases have recommendations been tested with prospective users. To address these gaps, this research provides a broad understanding of the barriers to accessing, and succeeding on, sandwich courses experienced by WP students – and to develop and test a Theory of Change to help remove the identified barriers.