Project Summary/Abstract Youth who exhibit an evening circadian chronotype (“night-owls”) follow a delayed sleep schedule, increasing activity later in the day and both going to sleep and getting up later, compared to morning types (“larks”). Eveningness arises from a confluence of psychosocial, behavioral and biological factors and is an important contributor to vicious cycles that escalate vulnerability and risk among youth. While the basic biological shift toward eveningness—initially triggered around the onset of puberty—may be difficult to modify, the psychosocial and behavioral contributors are modifiable. Supported by R01HD071065, we have conducted a “treatment experiment” in which we delivered the Transdiagnostic Sleep and Circadian Intervention for Youth (TranS-C) to reduce eveningness among 10-18 year olds. We randomly allocated youth with an evening chronotype, and who were “at risk” in at least one of five health-relevant domains (emotional, cognitive, behavioral, social, physical), to either: (a) TranS-C (n = 89) or (b) Psychoeducation (n = 87). While the results were promising, some drop off in treatment gains were observed. This is consistent with prior research documenting that a drop-off in the years following treatment is too commonly observed. Indeed, there have been calls to study if and how behavioral interventions are maintained (NOT-OD-19-040). Hence, in this revised renewal application, we propose to study the maintenance of behavior change by conducting a 6-year follow-up of the unique cohort of youth recruited for R01HD071065. The youth will be 16 to 26 years old. They will be assessed for sleep and circadian functioning and functioning in five health-relevant domains (emotional, cognitive, behavioral, social, physical) (SA1) and for their utilization of sleep health behavior (SA2). As a next step in this research program, we propose to evaluate if a Habit-based Sleep Health Intervention (“HABITs”)—a novel low-cost approach derived by leveraging the science of habit formation—improves the utilization of sleep health behavior and improves sleep and circadian outcomes and functioning in the five health-relevant domain outcomes in the short and longer term (SA3). An independent sample of youth who exhibit a high level of eveningness and are “at risk” in at least one of the five health-relevant domains will be randomly allocated to HABITs alone or HABITs plus Text Messaging (“HABITs+Texts”) (n = 160). The text messaging portion is derived from learning theory, the Behavior Change Wheel and focus groups. We will also examine if sleep health behavior that has become habitual mediates the effects of treatment on improvement in sleep, circadian and health outcomes. Moderation analyses will examine if intervention effectiveness is related to age/developmental stage, sex, SES, racial/ethnic minority group and season of participation. This research will advance knowledge on longer-term outcomes, the role of eveningness as a mechani...