Early morning university classes are associated with impaired sleep and academic performance.

"Competing interests The authors declare no competing interests."

"We thank researchers and students in the Chronobiology and Sleep Laboratory for collecting data; researchers and administrative staff at the National University of Singapore (NUS) Institute for Applied Learning Sciences and Educational Technology (ALSET) and NUS Information Technology (NUS IT) for supporting analyses of university-archived data; and F. M. Fung and E. S. Sugeng for facilitating the collection of instructor-reported attendance data. Data storage and management were supported by the NUS Office of the Senior Deputy President & Provost and ALSET. The work was funded by the Ministry of Education, Singapore (MOE2019-T2-2-074, J.J.G.) and the National Research Foundation, Singapore (NRF2016-SOL002-001, J.J.G.). The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript."

"The research complied with all relevant ethical regulations. Permission to analyse university-archived data was obtained from the National University of Singapore (NUS) Institute for Applied Learning Sciences and Educational Technology (ALSET). ALSET stores and links de-identified student data for educational analytics research on the ALSET Data Lake. University-archived datasets included students’ demographic information (age, sex, ethnicity, year of matriculation, country of citizenship, type of residence), course enrolment, Wi-Fi connection data, use of the LMS and grades. Analyses of these data were approved by the NUS Learning and Analytics Committee on Ethics (LACE). University and course characteristics are described in the . Students whose university-archived data were included in our study provided informed consent to the NUS Student Data Protection Policy, which explains that their data can be used for research. Analyses of university-archived data were exempt from review by the NUS Institutional Review Board (IRB) because they were performed retrospectively on data that were de-identified to the researchers. Permission for collecting attendance data from course instructors was approved by LACE. Research procedures in the actigraphy study were approved by the NUS IRB and students provided written informed consent to take part in the research. Participants were paid $250 in Singapore dollars for completing the actigraphy study. The research analytical approach was not registered in advance."