Based on the assumption that teaching behavior is influenced or determined by teachers' theories and beliefs of teaching, this study sought to examine how middle school science teachers perceive their instructional roles and how they go about improving their instructional effectiveness. Eleven teachers from two middle schools of the Midwest participated in the study. Classroom observations and formal and informal interviews with teachers, administrators, and students comprised part of the data sources. Reviews of texts, other instructional resources, tests, policy documents, and a series of three workshops provided additional data. About 350 science classes were observed by two researchers for 18 months. The findings are summarized in two sections in this report. The first section explains how it was determined if teachers were effective in presenting information and organizing learning activities. Observations on diagnostic and remediation efforts are reported in the second section. Generally, it was found that many teachers were ineffective in presenting and organizing information and in diagnosing student difficulties in learning science. Possible causes and consequences of this situation are outlined and implications are reviewed. A reference list is included. (ML)