This study tested and integrated the effects of an inquiry-based didactic method for preschool science in a real practical classroom setting. Four preschool classrooms participated in the experiment (N = 57) and the children were 4-6 years old. In order to assess children's attention for causal events and their understanding at the level of scientific reasoning skills, we designed a simple task in which a need for information gain was created. Compared to controls, children in the post-test showed significant learning gains in the development of the so-called control of variables strategy. Indeed, they executed more informative and less uninformative explorations during their spontaneous play. Furthermore, the importance of such programmes was discussed in the field of STEM education.