An exploratory study was conducted at the University of Southern Queensland (Australia) to document the knowledge of students held by a small number of highly effective primary school teachers and to identify the ways these teachers acquired their knowledge and used it during classroom instruction. This paper presents the findings of the investigation with one highly effective teacher who participated in the project. This teacher's knowledge of the class, student groups, and individual students was analyzed in terms of personality, interests, abilities, work habits, attributes, and behaviors. The teacher gathered knowledge about a student from parents, other students, classroom observation, working with the students, talking with her cooperative teaching partner, and reviewing formal school records. The teacher used this knowledge of students to develop students' social skills, to improve their work habits, to assist them with academic problems, and to direct their personality development. It is concluded that the teacher's teaching effectiveness might stem from the knowledge of her students, specifically the scope and depth of that knowledge, the classroom relevance, validity, integration and consistency, importance attached to knowledge of individual students, and ability to clearly articulate personal teaching philosophy. (Contains 19 references.) (JDD)