The Student Grouping Study: complex interventions require integrated mixed methods

The Student Grouping Study uses a matched design in a naturalistic context to explore the difference in student outcomes of two approaches to grouping students: grouping by ability (known as setting or tracking), and mixed attainment grouping (sometimes known as mixed ability grouping). Grouping practices can be characterised as a ‘complex whole-school intervention’, which may be implemented in different ways by schools. This results in the potential for significant variation in practice within and between the trial groups and a challenge for identifying and understanding the mechanisms of effective practice. We discuss how we have addressed these challenges through using theory-driven mixed methods, including surveys and in-depth case studies. We discuss how we have adapted implementation and process evaluation (IPE) guidance written for randomised controlled intervention trials, and present a set of principles for future, similar projects that are in line with guidance on high-quality IPEs.