Background: This work is based on the idea that young children benefit from early introduction of scientific concepts. Few researches describe didactical strategies focusing on physics understanding for young children and analyse their effectiveness in standard classroom environments. Purpose: The aim is to identify whether didactical strategies referring to a precursor model can be used to help children construct explanation of physical phenomena. Sample: We present results that test children's capacity (aged 5-6) to build knowledge within a precursor model in order to describe, explain and predict the phenomenon of shadow formation. Design and methods: The teaching intervention's efficiency is tested in a standard classroom setting. Data were collected through individual interviews, using identical tasks before and after the teaching intervention. Results: The analysis of children's ideas shows that the use of a constructivist didactical strategy referring to a precursor model of shadow formation by teachers has a positive effect on children's understanding and ability to identify shadows as a physical phenomenon. Conclusion: Such results support the importance of science teaching in preschools. In particular, the didactical strategy focuses children's attention to a critical aspect of their understanding and destabilizes their previous representations. It has implications for preschool teacher professional development.