Background: An open group climate is essential in successful residential care for juveniles with mild intellectual disability (MID). This study examined whether non-violent resistance, adapted for MID (NVR-MID), stimulates an open group climate in time. Method: NVR-MID was implemented in three residential settings in The Netherlands, in a quasi-experimental stepped wedge design. In total, 124 clients with MID (M[subscript age] = 16.39 [SD = 4.95], 49.9% male) participated. Group climate was assessed seven times with the Group Climate Inventory for Children or the Group Climate Inventory--Revisited (GCI-R), during a total of 20 months. Results: Open group climate scores increased in all three institutions; effect size was medium. Clients with lower IQs experienced group climate as more positive compared to clients with higher IQs. Effects were similar for both groups. Conclusions: As NVR-MID appeared to contribute to a positive experienced group climate, it might be advisable to implement NVR-MID on larger scale.