Student surveys are often used for school-based mental health screening; hence, it is critical to evaluate the authenticity of information obtained via the self-report format. The objective of this study was to examine the possible effects of mischievous response patterns on school-based screening results. The present study included 1,857 high school students who completed a schoolwide screening for complete mental health. Student responses were reviewed to detect possible mischievous responses and to examine their association with other survey results. Consistent with previous research, mischievous responding was evaluated by items that are legitimate to ask of all students (e.g., How much do you weigh? and How many siblings do you have?). Responses were considered “mischievous” when a student selected multiple extreme, unusual (less than 5% incidence) response options, such as weighing more than 225 pounds and having 10 or more siblings. Only 1.8% of the students responded in extreme ways to 2 or more of 7 mischievous response items. When compared with other students, the mischievous responders were less likely to declare that they answered items honestly, were more likely to finish the survey in less than 10 min, reported lower levels of life satisfaction and school connectedness, and reported higher levels of emotional and behavioral distress. When applying a dual-factor mental health screening framework to the responses, mischievous responders were less likely to be categorized as having complete mental health. Implications for school-based mental health screening are discussed.