An expert reading instruction teacher was studied for one academic year to explore his interactive decision making processes. Previous lines of research have indicated that, for some teachers, interactive decision making involves more than simply maintaining established routines that assure smooth activity flow and involves deviating from the pre-planned activities to attend to issues of content and pedagogy. In this study, Shavelson and Stern's models of preactive and interactive decision making were used to describe the expert teacher's actual performance. Specific examples of teacher-student interactions are given, with analyses of how they reflected the close relationship that existed between the teacher's preactive and interactive decision making and his knowledge, values, and beliefs about how reading should be taught. The study revealed that at least some teachers do make more interactive decisions during reading instruction. It also dramatized the relationship between preactive and interactive teaching, and the relationship between instructional plans and implementation of those plans. The study also emphasized that interactive decision making may not be a static phenomenon; rather, it takes different forms at different times of the academic year according to the function of instruction and the teacher's focus. The results support the Shavelson and Stern Models (1981) and suggest that those models are useful for explaining teacher decision making and planning further research. (JD)