Robust screening measures that perform well in different populations could help improve the accuracy of diagnosis of pediatric bipolar disorder. Changes in sampling could influence the performance of items and potentially influence total scores enough to alter the predictive utility of scores. Additionally, creating a brief version of a measure by extracting items from a longer scale might cause differential functioning due to context effects. The authors of current study examined both sampling and context effects of a brief measure of pediatric mania. Caregivers of 813 youths completed the parent-reported version of the General Behavior Inventory (PGBI) at an academic medical center sample enriched for mood disorders. Caregivers of 481 youths completed the PGBI at a community mental health center. Caregivers of 799 youths completed 10 items extracted from the PGBI at a community setting. Caregivers of 159 youths completed both versions of the PGBI and a semistructured diagnostic interview. Differential item functioning indicated that across samples some items functioned differently; however, total observed scores were similar across all levels of mania. Receiver operating characteristic analysis indicated that the 10 extracted items discriminated bipolar disorder from nonbipolar behavior as well as when the items were embedded within the full measure. Findings suggest that the extracted items perform similarly to the embedded items in the community setting. Measurement properties appear sufficiently robust across settings to support clinical applications. (Contains 2 figures and 4 tables.)