The purpose of this study is to evaluate the effect of a pretend play-based training in 5–6-year-old children in a large scale school context on emotion comprehension, emotion regulation, prosocial behaviour and on their pretend play competences. The analysis of implementation variables was carried out in order to ensure program implementation quality in the experimental group. Results show an improvement in emotion comprehension and a decrease in aggressive behavioural responses in children in the experimental group (n = 101) compared to those in the control group (n = 79). Findings are discussed in regard to implementation outcomes and the influence of this form of play on the improvement of these variables.