This report investigates the relationship between a broad range of pupil and school background factors and the KS4 [Key Stage 4] outcomes achieved by disadvantaged pupils. It looks at both the significance and strength of each association, in order to understand the relative importance of each factor in explaining differences in KS4 outcomes. The report also looks at the role of background characteristics in potentially explaining some of the progress gap between disadvantaged pupils and their more affluent peers. The research is based on a data supplied by DfE [Department for Education] from the National Pupil Database for all mainstream secondary pupils who sat their KS4 exams in 2016. Key findings from the 2015/16 cohort: (1) Variations in Progress 8 scores for disadvantaged pupils were most strongly associated with a pupil's absence rate during KS4, their exclusion rate during secondary school and whether or not they moved schools during KS4; (2) Variations in Attainment 8 scores for disadvantaged pupils were most strongly associated with a pupil's KS4 absence rate, KS2 attainment and Special Educational Needs and Disabilities (SEND) status; (3) The average absence and movement rates of a pupil's year group were associated with the variation in KS4 outcomes of disadvantaged pupils in that group; (4) 55 per cent of the gap in Progress 8 scores, between disadvantaged pupils and their more affluent peers, can be explained by the between-group differences in absence, exclusion and KS4 movement rates during secondary school at both pupil and cohort level; and (5) 30 per cent of the gap in Attainments 8 scores, between disadvantaged pupils and their more affluent peers, can be explained by the between-group differences in absence, exclusion and KS4 movement rates during secondary school, along with differences in their KS2 scores, at both pupil and cohort level.