This randomised controlled trial investigated the effects of a student-led progressive resistance training (PRT) programme in adolescents and young adults with Down syndrome. Sixty-eight young people with Down syndrome (30 female, 38 male; mean age 17.9±2.6 years) and mild to moderate intellectual disability were randomly allocated to a PRT programme (n=34) or a social group (n=34). Participants in the PRT group trained twice a week for 10 weeks at a community gymnasium with a physiotherapy student mentor using pin-loaded weight machines. Participants in the social group completed a 10-week programme of social activities also with a student mentor once a week for 90 min. Work performance, muscle strength and physical activity levels were assessed at weeks 0, 11 and 24 by an assessor blind to group allocation. Data were analysed using ANCOVA with baseline measures as covariate. Participants attended 92% of their scheduled sessions. There was no difference between the groups on work task performance. The PRT group increased their upper and lower limb strength at week 11 compared to the control group, but only their lower limb muscle strength at week 24. There was a significant difference in physical activity levels in favour of the PRT group at week 24 but not at week 11. PRT using a student mentor model helps young people with Down syndrome become stronger and more physically active but its effect on work task performance is unclear.