The present observational study was designed to evaluate the effectiveness of the I Can Problem Solve (ICPS) programme on behavioural change from aggression to pro-social behaviours by using the DECB rating scale. Non-participant observation method was used to collect data in pretest-training-posttest design. It was hypothesised that the ICPS programme would be useful to decrease in aggressive behaviours, increase in pro-social behaviours and also to improve in introverted behaviours. In total, 83 five- and six-year-old children attending public preschools participated in the study. Pro-social and introvert behaviours of children in the experimental group were significantly improved compared to the control group. Although there was no significant difference statistically between pretest-posttest scores of experimental and control group, the mean scores of both groups differentiated considerably. (Contains 3 figures and 3 tables.)