Baseline quantitative survey data collected as part of the Better Sleep Better Health study. It contains data on 358 participants in two schools, with baseline data collected through a self-completed survey with items on sleep health and insomnia (using the Cleveland Adolescent Sleepiness Questionnaire, Munich Chronotype Questionnaire and Insomnia Severity Index (ISI)) and mental health with the UNICEF Measuring Mental Health Among Adolescents and Young People at the Population Level (MMAPP) tool.