This study examined the relationship between the complexity of thinking about children by child care teachers and observed teachers' caregiving for infants and toddlers. It was hypothesized that the perceived supportiveness of the work environment would affect this relationship. Fifty-six child care teachers completed a survey assessing complexity of thinking about children's behaviour as well as a measure of the perceived opportunities for professional development. Teachers' quality of caregiving was assessed using the "Caregiver Interaction Scale." Planned contrasts revealed that when professional development opportunities were perceived "unfavourably," teachers who were complex in thinking about children's behaviour provided significantly more sensitive care than did teachers who were less complex in their thinking. Findings indicate that the complexity of teachers' thinking about children may be very important in understanding teacher's sensitivity when the quality of the work environment is poor. High-quality work environments may buffer teachers with less complexity of thinking from being less sensitive with children. Efforts to improve quality of care could focus on individual teachers to improve their complexity of thinking as well as on the work environment to make it more supportive of teachers' professional development. (Contains 4 tables.)