This study explored whether early childhood preservice teachers' concerns about teaching nature of science (NOS) and their intellectual levels influenced whether and how they taught NOS at the preschool and primary (K-3) levels. We used videotaped classroom observations and lesson plans to determine the science instructional practices at the preschool and primary levels, and to track whether and how preservice teachers emphasized NOS. We used the Stages of Concern Questionnaire (SOCQ) pre- and postinternship to determine concerns about NOS instruction, and the Learning Context Questionnaire (LCQ) to determine intellectual levels. We found that neither concerns about teaching NOS nor intellectual level were related to whether and how the preservice teachers emphasized NOS; however, we found that all preservice early childhood teachers began their internships with NOS concern profiles of "worried." Two preservice teachers' NOS concerns profiles changed as a result of their internships; one to "cooperator" and one to "cooperator/improver." These two preservice teachers had cooperating teachers who were aware of NOS and implemented it in their own science instruction. The main factors that hindered or facilitated teaching NOS for these preservice teachers were the influence of the cooperating teacher and the use of the science curriculum. The preservice teacher with the cooperating teacher who understood and emphasized NOS herself and showed her how to modify the curriculum to include NOS, was able to explicitly teach NOS to her students. Those in classrooms whose cooperating teachers did not provide support for NOS instruction were unable to emphasize NOS. (Contains 1 table.)