American teenagers spend about an hour on their smartphones during school hours, according to data from the Adolescent Brain Cognitive Development (ABCD) study.[3][4] The study used passive measurement via a smartphone app in 67 children aged 11-12 years (46% girls, 34% Caucasian) over 4 weeks in 2019-2020.[3][4] Objective data showed average daily usage: streaming 1 hour 57 minutes (SD 1 hour 32 minutes), communication 48 minutes (SD 1 hour 17 minutes), gaming 41 minutes (SD 41 minutes) and social networking 36 minutes (SD 1 hour 7 minutes).[4] Children underestimated their use compared to objective data (correlation value r=0.49).[3][4] Self-reported use was partially consistent with measurement, but children reported less time than actual.[4] Before the measurement, 21% of children (14/66) reported using the phone more than their peers, after the measurement this dropped to 13% (8/62).[3] The study recommends more robust objective methods to accurately assess the impact of smartphones on behavior and emotions.[4]