The authors argue that part of the difficulty in studying the teaching of reading in elementary classrooms is determining where 'the action' occurs in reading instruction. Based on their 5-year longitudinal study, they describe three challenges: (a) determining key factors in the complex instructional environment that should be the focus of study, (b) determining who teaches reading to specific students, and (c) determining the boundaries of reading instruction or when it occurs during the school day and year.