It is acknowledged internationally that teachers’ Professional Development (TPD) is crucial for reforming science teaching. The Danish QUEST project (“Qualifying in-service Education of Science Teachers”) is designed using widely agreed criteria for effective TPD: content focus, active learning, coherence, duration, collaborative activities and collective participation, and organised on principles of situated learning in Professional Learning Communities (PLCs). QUEST-activities follow a rhythm of full day seminars, where teachers are introduced to research-based material followed by a period of collaborative inquiries locally. A major theme in the first year has been Inquiry Based Science Education (IBSE) recommended as a focus to improve science education internationally. The research presented focuses on the participating teachers’ intertwined levels of individual and social learning. Data from repeated surveys and case studies reveal a positive attitude towards trying IBSE in the own classroom, however with the main part of the reflections focused on students’ hands-on experiences and fewer including students manipulating science ideas, like posing hypotheses. Teachers’ reflections indicate that many are positive toward IBSE-seminars based on trying activities directly applicable in the classroom. Other teachers’ reflections, and case-studies, indicate a potentially more sustainable development, where they collaboratively re-design former teaching using the IBSE thinking - and by doing so gaining experiences to support their design of inquiry based learning experiences for students also in new content areas. Case studies support that the PLCs are developing a new focus on student learning, but 25 % of the teachers report little change in collaboration locally with case studies identifying challenges related to disseminating IBSE to colleagues. Factors supporting or hampering local sustainable development are discussed under the headlines 1) QUEST rhythm, 2) Research knowledge meeting practitioner knowledge and 3) Individual and collaborative agency.