This study tests the explanatory power of Deci and Ryan's (1985) self-determination theory as a framework for describing how interactions between early childhood teachers and the systems within which their work is embedded influence motivation for professional growth and change in teaching practice. Fifty-four early childhood teachers and teacher assistants participated in a yearlong professional development program comprising monthly workshops and on-site support visits. Quantitative analysis of motivation and work attitude surveys, coupled with qualitative analysis of teacher interviews, addressed two major research questions: (1) What factors within the social context of early childhood teachers' workplaces are related to their motivation for professional growth? and (2) What is the relationship between early childhood teachers' motivation for professional growth and change in teaching practice? Results indicate that three facets of work satisfaction were significant predictors of intrinsic interest in professional development: supervisor support, the nature of the work itself, and co-worker relations. The qualitative analysis reveals ways in which interactions between motivation, professional development activities, and work environment support or undermine change. (Contains 6 tables, 1 figure and 1 note.)