The purpose of this study was to learn whether Science Curriculum Improvement Study (SCIS) or more recent interpretations of the learning cycle could be used by teachers to engage students in social constructivist learning. To accomplish this purpose, two university researchers and six science teachers planned, implemented, and reflected upon instruction based on the reciprocal use of language and action within the learning cycle framework. The study examined teachers' changing beliefs and practices as well as issues and problems that emerged. Discrepant case analysis was used to analyze the data, which included transcriptions of instruction, reflection sessions, and teacher and student interviews as well as copies of teachers' written plans and instructional materials. In this paper, we present a case study of one teacher and profiles of five others. The case is organized chronologically and describes Martha, a high school physics teacher, in terms of her instruction and concerns at the beginning, middle, and end of the school year. Analysis revealed that several of Martha's beliefs and practices gradually changed across the year. Martha initially expressed the positivistic view that the goal of science instmction was for students to arrive at scientifically acceptable conclusions. As Martha explored social constructivist teaching, she gave her students increasingly more opportunities to test and discuss their ideas during problem solving. Along with this change in practice, Martha experienced a tension between her efforts to give her students opportunities to develop their own understandings and her efforts to present scientific information. As Martha' perspective changed, she became dissatisfied with her existing grading system. Like Martha, each of the other five teachers gave their students more opportunities to explore their own ideas and each experienced tensions in the process. We interpreted these findings within a social constructivist theoretical framework to suggest changes in the learning cycle.