This study examined the teacher's role in creating a gender-sensitive environment in an all girls physics class and the effects of that environment on girls' achievement, self-concept, and career choices. Reflective journaling by the teacher-researcher was used to discover, analyze, and challenge appropriate teaching strategies and personal biases. Extensive descriptions of the daily operation of the class are employed in an ethnographic methodology to develop a portrait of a classroom environment that is evolving, while revealing its gender sensitive and gender bias aspects and their effects on the girls. Additional data sources include student work, pre- and post-class surveys, student journals, informal conversations with students, and post-class interviews. The vignettes, field note descriptions, and excerpts from reflective journals included describe the growth and development of the girls and the teacher. Findings indicate that each intersection of girls' needs and the teacher's role demonstrated the twin requirements of teacher recognition of the girls' needs and teacher knowledge of intervention strategies to address the need, fulfill the expectations of the girls and the teacher, and create the environment necessary for continued growth and learning. It was concluded that the factors identified in the literature as critical to girls in their science education are evident in a gender-sensitive classroom. (JRH)