Education is a key driver of intergenerational mobility, yet previous research has suggested that there are large socio-economic and ethnic gaps in higher education participation, including amongst the most selective institutions. Prior attainment has been found to be an important reason why some young people are more likely to go to university than others, but it is less clear which stage of education has the greatest impact on HE participation. This is vital from a policy perspective, as it provides insight into the best time to intervene to raise participation. This report uses linked individual-level administrative data from schools in England and universities in the UK to document the relationships between socio-economic status, ethnicity and HE participation, and explore what drives these relationships.