E-readers are becoming a common tool in the classroom, yet little is known about how teachers and students are using these tools to support reading motivation and comprehension. Drawing on sociocultural theory and data collected from fourth-grade teachers and students, we find that teachers used e-readers to monitor student comprehension of assigned readings, but provided little motivational support. While this instructional approach helped students self-regulate their learning, it was disruptive to students' reading enjoyment and contributed to adverse learning behaviors. We situate these findings in rich contextual detail on teachers and students. Our findings shed light on affordances and constraints that teachers can experience when using e-readers for instruction.