A popular concept in education indicates that effective instruction requires the teacher to know the child. A study was conducted at the University of Wisconsin-Milwaukee in order to determine where this knowledge comes from. A group of 15 teachers enrolled in the graduate school listed their students and indicated which students they knew something about or knew nothing about. They then predicted which students would be the top three in the class and which would be the bottom three. At the end of the semester a second exercise was completed in which they indicated the sources of knowledge about each student. Findings suggest that when the teacher does know more about the child, such knowledge does not come directly from the child but rather from parent conferences, student records, other teachers, or school specialists. Furthermore, these teachers knew almost nothing about one-third of the 372 students involved in the study. It can be recommended that teachers first learn more about their students from the students themselves and supplement this knowledge by interacting with the students' home life. The question which serves as the title of this article is still largely unanswered. Tables depicting four elements of teacher/student knowledge are included. (LL)