Early elementary school start time: impact on sleep, health, and learning

The National Heart, Lung, and Blood Institute awarded Rush University Medical Center $783,899 on July 5, 2026, under the Cardiovascular Diseases Research program (CFDA 93.837) to examine the impact of early elementary school start times on sleep health, learning, attention, and obesity in young children through second grade.

The study enrolls 200 kindergartners—50 night owls and 50 morning larks attending early-start schools (by 8:00 a.m.), and 50 night owls and 50 morning larks attending late-start schools (after 8:00 a.m.)—and follows them through second grade to assess cumulative effects. For a subset of 50 kindergartners in the first study year, baseline circadian phase will be measured through salivary melatonin (dim light melatonin onset) to validate chronotypes established by behavioral measures. Across all participants, sleep and wake behavior will be measured annually via wrist actigraphy and validated questionnaires assessing sleep health and chronotype. Participants complete annual reading, math, and attention assessments; parents complete annual child-sleep quality questionnaires; teachers provide annual learning and attention reports.

The research is motivated by preliminary findings showing negative effects of early school start times for young night owls, particularly given that up to 30 percent of the population, including young children, display later sleep and wake inclinations. The study addresses the absence of data on whether early start times harm young learners, including kindergartners, as schools nationwide shift toward evidence-based later start times for middle and high school students.

Performance occurs in Chicago, Illinois. The period of performance runs through June 30, 2031.

Abstract

Many U.S. Schools are shifting start times earlier for elementary students to accommodate a national shift toward evidence-based later start times for middle and high schoolers. This shift, however, is occurring despite the absence of data showing whether early start times are harmful to young learners, including kindergartners. Up to 30% of the population, including young children, are considered "night owls", meaning that they are inclined to sleep and awaken later. Uniformly imposing early start times in elementary schools, under an assumption of no harm, may pose unanticipated risks for circadian misalignment, sleep deprivation, learning and attention challenges, and obesity for many young night owls. Supported by our preliminary findings of a negative effect of early school start times for young night owls, the overarching goal of this proposal is to determine the impact of early school start times on sleep health, learning and attention, and obesity in 200 kindergartners and to follow them through second grade to examine cumulative effects on outcomes. We will enroll 50 kindergartner night owls and 50 kindergartner "morning larks" who attend early-start schools (by 8:00 A.M.), and 50 kindergartner night owls and 50 kindergartner morning larks who attend late-start schools (after 8:00 A.M.). Baseline circadian phase will be measured through salivary melatonin (DIM light melatonin onset) for a subset of participating 50 kindergartners during their first study year to evaluate the concordance of chronotypes established by behavioral measures. For all study participants, sleep/wake behavior will be measured via wrist actigraphy and validated sleep health and chronotype questionnaires annually. Participants will also complete reading, math, and attention measures annually. Parents will complete child-sleep quality questionnaires annually. Teacher-report of learning and attention will be collected annually, each winter or spring, based on enrollment date. Obesity will be assessed via calculated body mass index (BMI)-for-age percentile and obesity-promoting routines through parent-report annually. These study outcomes will allow US to examine the following specific aims to achieve our goal: aim 1. Determine whether sleep health outcomes (school day sleep duration, weekend midpoint, weekend oversleep, social jetlag, and daytime sleepiness) differ between night owls and morning larks in early and late start elementary schools. Aim 2. Determine whether learning (reading and math scores) and attention differ between night owls and morning larks in early and late start elementary schools. Aim 3. Determine whether night owls exhibit greater risk for obesity (BMI-for-age percentile) and obesity-promoting routines compared with morning larks in early and late start elementary schools. Results of our study may inform educational policy to better support healthy start times for all students.