Background: Transition Year (TY) is a quasi-gap year offered midway through post-primary education in Ireland. TY is intended to provide a low-stakes environment to promote maturity and social skills, and to prepare students for adult life. Previous interview-based research has found that TY is seen as a positive experience by many students and teachers. However, no study has sought to quantify the extent to which TY participation may be associated with socioemotional development. Aims: To gather baseline data before TY and then examine differences in socioemotional outcomes over a 2-year period (three waves of data collection) between students who went on to take part in TY and those who did not. Sample: A total of 1,563 Grade 9 students ?(47% female, mean age = 15.4 years) in 20 schools were randomly sampled to provide a nationally representative sample. Methods: Outcome measures were selected to reflect (1) the intended aims of TY and (2) outcomes consistently identified through qualitative research as being associated with TY. These include student--teacher relations, self-reliance, subjective age, school satisfaction, and social self-efficacy. Latent growth curve models were used to examine differences in students' development over time, controlling for initial (baseline) status and background covariates. Results: TY participants reported significantly higher increases in subjective age and (for boys) self-reliance over three waves than non-participants. However, expected differences were not observed for other measures. Conclusions: This is the first study to report longitudinal quantitative analyses of socioemotional outcomes in TY. The results highlight a tension between broadly positive qualitative reports of TY outcomes and the limited quantitative evidence, to date, of same. Some directions for future research are suggested.