This article focuses on impacts of collaborative action research with a spiral process of planning, acting, observing, and reflecting that had been used as a strategy to promote teacher professional development in science education of Thailand. With the school principals' support, three primary science teachers' instructional practices are the subject of individual case studies. A range of qualitative methods and data sources including participant observations, individual and collective interviews, teacher and student artifacts were adapted to elicit evidence related to change of teaching practices and perceptions on action research activities. The case study analysis showed that collaborative action research enabled the primary science teachers to change their teaching practices within the classroom conditions. Factors that were identified as important to these changes included: (1) the primary teachers needed school leadership that powerfully attends to their professional development activities; and (2) the teachers needed a university coach to collaboratively reflect and suggest how to teach in the particular subject i.e. science. In the case of a primary teacher who, having no qualifications (i.e., certification-related teacher preparation) in science teaching, additionally needed a community of professional teachers willing to collaboratively reflect on classroom experiences for better inquiry into science teaching practices. As a means to sustain the changes in this educational context, implementing the collaborative action research while providing opportunities for parents to observe and reflect upon teachers' classroom teaching practices was also found to be important.