The focus of this study was to investigate the manner and the degree to which science teachers consider the nature of the subject matter in their decision making addressing the planning and the delivery of instructional tasks. An assumption of the study is that considerations for the nature of the subject matter should be a factor in a teacher's decision making about what to teach and how to teach. Relevant research literature reviewed includes (1) human decision making and the development of cognitive models of reality, (2) modern philosophies of science, and (3) philosophy of science and science education. Methods of data collection and of data analysis followed Spradley's Developmental Research Sequence guidelines for conducting ethnographic research. Validity of research findings was established from the triangulation of observations, interviews, and documents and surveys. The goal of the research was the development of grounded hypotheses about science TEACHERS' pedagogical decision making. Based on the results of this study it is hypothesized that science TEACHERS' decision-making models of reality for the selection, implementation, and development of instructional tasks are dominated by considerations for (a) student development, (b) curriculum guide objectives, and (c) pressures of accountability. Little, if any, consideration is given to the nature of the subject matter by the science teachers in decision making. Implications exist for the disenfranchisement of teachers from the task of making decisions concerning what to teach.