Materials designed to improve parental monitoring were distributed to 33,000 parents of intervention middle and high school students. Additional distribution to parents of incoming 6th and 9th graders occurred between Time 2 and Time 3. Among all students, reports of specific monitoring strategies (e.g., rules about friends and dating) increased (p<.0001) from baseline to Time 3. Although the increase from baseline to Time 2 was significant among comparison students (p<.05), the change from Time 2 to Time 3 was not. In contrast, the increase among intervention students was more pronounced (p < .05), with a significant increase at each wave.