The focus of this chapter is squarely on the impact of different grouping practices on pupil outcomes. Given the research literature on attainment outcomes was analysed in Chapter 2, this chapter attends especially to the impact of attainment grouping on self-confidence. We begin by looking at explanations for the established trends precipitated by attainment grouping on pupil attainment outcomes. Then our findings with respect to the nature and extent of the relationship between set allocation and self-confidence are discussed. The analysis establishes significant relationships between set level and pupil self-confidence – for both of the key curriculum subjects of maths and English, and for general self-confidence in learning. These trends for lower self-confidence for low-set pupils and greater self-confidence for those in high sets are exacerbated over time, suggesting a causal effect of attainment grouping. The qualitative data suggest that young people are aware of the labelling effects of setting, and indeed many of them volunteered accounts of self-fulfilling prophecy precipitated by attainment grouping.