This study assessed, and identified factors in participants' learning ecologies that mediated, the effectiveness of an explicit reflective instructional approach that satisfied conditions for learning as conceptual change on preservice elementary teachers' views of nature of science (NOS). Participants were 28 undergraduate students enrolled in an elementary science methods course. A purposively selected focus group of six participants who showed differential growth in terms of their NOS views were closely followed throughout the study. The "Views of Nature of Science Questionnaire-Form B" (VNOS-B) in conjunction with individual interviews was used to assess participants' views prior to and at the conclusion of the study. Other data sources included weekly reflection papers, exit interviews, and an instructor's log. Initially, the greater majority of participants held naive views of NOS. Substantial and favorable changes in these views were evident as a result of the intervention. An examination of the development of the focus group participants' NOS views indicated that the effectiveness of the intervention was mediated by motivational, cognitive, and worldview factors. These were related to internalizing the importance and utility of teaching and learning about NOS, exhibiting a deep processing approach to learning, and viewing science and religion as two distinct rather than opposing enterprises.