Kindergarten retention is a popular practice for children who are considered unready for primary school. However, past research has not yet succeeded to find consistent, strong empirical evidence supporting the practice. In the current study, kindergarten repeaters' development in nine psychosocial domains is compared with that of equally at risk but (1) continuously promoted age-mates and (2) promoted age-mates who repeated first grade instead. Analysing data from a large-scale longitudinal study using propensity score matching and multilevel modelling, the findings reveal no harm of kindergarten retention for at-risk children's long term psychosocial development. Rather, we find that, relative to equally at-risk but continuously promoted children, kindergarten repeaters benefit from retention with respect to higher levels of well-being, and peer relations, and lower levels of hyperactivity, aggression and asocial behaviour. Compared to similar children who were promoted but who were retained in first grade instead, kindergarten repeaters are found to benefit more from retention with respect to higher levels of well-being, self-confidence, attitude to work and independent behaviour, and lower levels of hyperactivity.