The impact of self-fulfilling prophecy in education, and of attainment grouping on pupil self-perception, remain topics of longstanding debate, with important consequences for social in/justice. Focusing on self-confidence, this article draws on survey responses from 9,059 12-13 year olds who were tracked by subject ('setting'). They provided survey responses when placed in 'ability' sets at the start of their secondary schooling, and again late the following year; enabling analysis of impact over time. After controlling for prior attainment, the gap in general self-confidence between students in the top and bottom sets for mathematics is shown to widen over time, and high set students' self-confidence in English had also grown significantly; although there was not further widening in the cases of self-confidence in mathematics or in general self-confidence between students in the top and bottom sets for English. Implications of these findings for interventions directed at addressing educational disadvantage are discussed.