Conveying an adequate conception of the nature of science to students is implicit in the border context of what has come to be known as scientific literacy. However, it has previously been demonstrated that possession of valid conceptions of the nature of science does not necessarily result in the performance of those teaching behaviors that are related to improved student conceptions. The present study examines the possibility that the language teachers use to communicate science content may provide the context (Realist or Instrumentalist orientations) in which students come to formulate a world view of science. Eighteen high school biology teachers and one randomly selected class from each of their sections (n = 409 students) were administered pre- and posttests at the beginning and end of the fall term using the Nature of Scientific Knowledge Scale (NSKS). Composite scores of the student changes on the Testable, Developmental, and Creative subscales were used to compare those six classes that exhibited the greatest change with those six classes that had the least change on the NSKS. Intensive qualitative observations of each teacher were also conducted over the fall semester, resulting in complete transcripts of teacher-student interactions. Qualitative comparisons of classes with respect to six variables related to Realist and Instrumentalist conceptions of the nature of science were conducted. TEACHERS' ordinary language in the presentation of subject matter was found to have significant impact on students' conceptions of the nature of science. These variables represented different contexts (Realist-Instrumental) teachers used to express themselves, scientific information, and concepts. Determining the extent to which TEACHERS' language has an impact on changes in students' conception of the nature of science has direct bearing on all preservice and inservice science teacher education programs.