This study explores the specific characteristics of teacher-educator professional development interventions that enhance their transformative learning towards stimulating the inquiry-based attitude of students. An educational design research method was followed. Firstly, in partnership with five experienced educators, a professional development programme was designed, tested and redesigned. Secondly, a qualitative multiple case study was conducted to examine the active ingredients of the designed interventions with regard to educators' changes in beliefs and behaviour. The study was carried out in four different educational settings in which 20 educators participated during nine months. Data sources included videos, questionnaires, interviews and written personal theories of practice. The analyses indicated that aligned self-study interventions on a personal, peer and group level guided by a trained facilitator supported the intended leaning.