Background : This study aims to examine the effects of STEM activities, focused on inquiry-based learning, on pre-service elementary teachers’ subject matter knowledge about sound phenomena and concepts. A qualitative and interpretive methodology was used. Setting and Participants : The participants are nine pre-service teachers, studying in a Portuguese Higher School of Education. These pre-service teachers were enrolled in the Chemistry and Physics Sciences course in the first year of the Degree in Basic Education. Data collection and analysis : Two data collection methods were used: (i) students’ productions developed through six STEM activities that included concepts about sound, such as production of sound vibration, wave, transmission, velocity, and loudness and (ii) field notes collected by the first author of this article. To analyse the data, an inductive strategy of content analysis was used. Results : Results showed that pre-service teachers revealed many misconceptions about concepts of sound and pointed to an evolution on pre-service teachers’ subject matter knowledge. These results demonstrated that the STEM approach favoured an active involvement of pre-service teachers in their learning, connecting contents to real-life. Conclusions : Results encourage further research on the impacts of a STEM approach in PTs pedagogical content knowledge.