Guided by self-determination theory, this study investigated the extent to which factors of teachers' school-work environments predict their self-efficacy and intrinsic value for teaching. Participants were 217 mathematics teachers working in Texas public schools. Results indicated that principals' autonomy support positively predicted teachers' self-efficacy and intrinsic value for teaching beyond years of teaching experience, mathematics background, and grade level taught. Moreover, the negative effects of school-work environments dominated by high-stakes testing on teachers' motivation for teaching were moderated by the level of autonomy support provided by the school principal.