Given the consensus on the importance of teacher reflection and the paucity of research on affective motivational challenges and outcomes of in-service teacher reflection, this study examined the hypothesis that support of in-service teachers' basic psychological needs (for relatedness, competence, and autonomy) in collaborative reflection settings would predict increased reflectivity, which, in turn, would predict increased autonomous motivation for and sense of accomplishment in teaching. Employing self-determination theory, we analyzed beginning- and end-of-year data from 92 Israeli in-service teachers participating in a programme designed to promote collaborative reflective inquiry. The results confirmed our hypothesis, suggesting facilitators' support for teachers' psychological needs may foster teacher reflection and, consequently, their motivation for teaching, with implications for teachers' well-being, and the quality of their professional learning and their teaching. The findings provide evidence that psychological challenges in promoting in-service teachers' reflection can be overcome and offer a theoretical framework for designs that contend with these challenges. This study adds to research on reflection by suggesting reflection may improve teaching by bolstering teachers' motivation. It adds to teacher motivation research by suggesting teacher motivation is malleable, even for veteran teachers, and may be fostered through properly designed PD.