Why autonomy-supportive interventions work: Explaining the professional development of teachers' motivating style

•Post-intervention, teachers' motivating style became more autonomy supportive.•During the intervention, teachers developed three personal-professional resources.•Intervention-enabled gains in teaching efficacy explained greater autonomy support.•Intervention-enabled gains in intrinsic goals explained greater autonomy support.

Carefully designed interventions consistently help K-12 teachers learn how to implement a more autonomy-supportive classroom motivating style. In the present study, we investigated what resources teachers acquired during these interventions that explained why they are so able to successfully upgrade the quality of their motivating style. We randomly assigned 91 full-time teachers to participate or not in a year-long autonomy-supportive intervention program (ASIP), and we longitudinally assessed autonomy support and three hypothesized mediating resources-gains in need satisfaction during teaching, gains in teaching efficacy, and a greater adoption of intrinsic instructional goals. The ASIP did increase teachers' autonomy support, as expected, and the two resources that explained this professional developmental achievement were intervention-enabled gains in teaching efficacy and intrinsic instructional goals.