This research clarifies how a collaborative team teaching model (CTTM) can support both pre-service and in-service teachers' professional development in using inquiry-based science teaching in primary schools. The data were collected via a questionnaire-based survey approach after inquiry projects implementation at public schools in four Finnish cities. In total, 98 pre-service teachers and 51 in-service class teachers were involved in the research. According to their experiences collaborative team teaching was seen as an adequate teaching approach in primary school science lessons. Both in-service and pre-service teachers experienced inquiry-based science teaching enthusiastically and received new ideas, knowledge and skills to carry out inquiries during the school projects. Also, they became more confident to use inquiry-based approach in their teaching. The findings indicate that the CTTM combines pre-service teachers' professional development and in-service teachers' expertise and the model successfully support the use of inquiry-based practices in primary school science education.