While most educators assume that not all students try their best on achievement tests, no current research examines if behaviors associated with low test effort, like rapidly guessing on test items, affect teacher value-added estimates. In this article, we examined the prevalence of rapid guessing to determine if this behavior varied by grade, subject, and teacher, and evaluated if rapid guessing influenced teacher value-added estimates. We observed differences in rapid guessing across grades, subjects, and teachers; however, this behavior did not appear to have a substantive effect on teacher value-added estimates. These findings suggest that rapid guessing occurs frequently enough that educators should be mindful of its effect on the interpretations of student test results. However, based on the value-added specifications used in this research, this type of behavior did not appear to affect estimates of teacher performance.