To achieve quality education in American schools, we need a better understanding of the way classroom instruction works. Susan S. Stodolsky addresses this need with her pioneering analysis of the interrelations between forms of instruction, levels of student involvement, and subject matter. Her intensive observation of fifth-grade math and social studies classes reveals that subject matter, a variable overlooked in recent research, has a profound effect on instructional practice. Stodolsky presents a challenge to educational research. She shows that classroom activities are coherent actions shaped by the instructional context—especially what is taught. Stodolsky contradicts the received view of both teaching and learning as uniform and consistent. Individual teachers arrange instruction very differently, depending on what they are teaching, and students respond to instruction very differently, depending on the structure and demands of the lesson. The instructional forms used in math classes, a "basic" subject, and social studies classes, an "enrichment" subject, differ even when the same teacher conducts both classes. Social studies classes show more diversity in activities, while math classes are very similar to one another. Greater variety is found in social studies within a given teacher's class and when different teachers' classes are compared. Nevertheless, in the classrooms Stodolsky studied, the range of instructional arrangements is very constricted. Challenging the "back to basics" movement, Stodolsky's study indicates that, regardless of subject matter, students are more responsive to instruction that requires a higher degree of intellectual complexity and performance, to learning situations that involve them in interaction with their peers, and to active modes of learning. Stodolsky also argues that students develop ideas about how to learn a school subject, such as math, by participating in particular activities tied to instruction in the subject. These conceptions about learning are unplanned but enduring and significant consequences of schooling. The Subject Matters has important implications for instructional practice and the training, education, and supervision of teachers. Here is a new way of understanding the dynamics of teaching and learning that will transform how we think about schools and how we study them.