This paper presents results of the evaluation of a programme for the development of social skills, called 'Play Time/Social Time' (PTST; Odom et al. 1997), undertaken in Polish pre-schools. Over 150 pre-schoolers participated in the intervention: children with disabilities (autism, intellectual, physical, and sensory disabilities), children with low social skills but without disabilities, as well as normally developed children. We observed whether there are changes in children's social skills after participation in the PTST programme. We assessed the effectiveness of the intervention by using growth curve modelling and repeated-measures ANOVA. Both methods demonstrated positive effects of the programme with high effect size. Additionally, we found the PTST to be especially effective in developing social skills of children with disabilities and with low social skills. These findings provide potentially important consequences for the development of social skills among children with disabilities and children who display behavioural problems. Specifically, it demonstrates that the PTST, as a very effective programme, may be introduced among very young children. (author abstract)