{
  "type": "fact",
  "url": "https://karelbusta.dev/data/sleep/later-school-start-more-sleep",
  "title": "Starting school 55 minutes later gave Seattle teens 34 more minutes of sleep",
  "claim": "After Seattle moved high-school start time from 07:50 to 08:45, students' median wake-up on school days moved 44 minutes later and their median school-night sleep grew by 34 minutes, measured with wrist actigraphy.",
  "description": "Seattle's 55-minute later high-school start brought a 34-minute increase in median school-night sleep, measured with wrist actigraphy.",
  "confidence": "single study",
  "published": "2026-10-14",
  "context": "The worry with later school starts is that teenagers will simply stay up later. In Seattle, bedtimes barely moved, so most of the extra morning time became sleep. On free days nothing changed, which points to the schedule as the cause. Median second-semester grades rose from 77.5% to 82%, and daytime sleepiness fell. First-period absences and late arrivals dropped at Franklin High, the more economically disadvantaged of the two schools, but not at Roosevelt. Caveats: this is one district and two schools, the before and after groups were different students, and there was no control group that kept the early start. Earlier survey-based studies point the same way, but this was the first to show the effect with objective sleep recordings.",
  "sources": [
    {
      "authors": "Dunster GP, de la Iglesia L, Ben-Hamo M, Nave C, Fleischer JG, Panda S, de la Iglesia HO",
      "journal": "Science Advances",
      "sampleSize": "178 sophomores at two Seattle high schools (94 in spring 2016, 84 in spring 2017), 2 weeks of actigraphy each",
      "title": "Sleepmore in Seattle: Later school start times are associated with more sleep and better performance in high school students",
      "url": "https://doi.org/10.1126/sciadv.aau6200",
      "year": 2018
    }
  ],
  "method": "For the 2016–2017 school year, the Seattle School District moved secondary-school start time from 07:50 to 08:45. The researchers ran a pre/post comparison. In spring 2016 (before) and spring 2017 (after), sophomores taking the same science class at two high schools wore wrist activity monitors for two weeks and kept sleep diaries. The two years used different students, compared at the same point in the school year. School-day medians were compared with Wilcoxon tests corrected for multiple comparisons. Each student contributed at least five school nights.",
  "chart": {
    "data": [
      {
        "label": "School start time",
        "value": 55
      },
      {
        "label": "Wake-up on school days (median)",
        "value": 44
      },
      {
        "label": "Sleep on school nights (median)",
        "value": 34
      }
    ],
    "highlight": [
      "Sleep on school nights (median)"
    ],
    "note": "Results text. Start time 07:50 → 08:45. Median sleep offset 06:24 → 07:08 (+44 min, P < 0.0001). Median school-day sleep duration +34 min (P = 0.0007). Sleep onset showed only a non-significant trend toward later.",
    "title": "What changed when Seattle high schools started later",
    "type": "column",
    "unit": "min",
    "x": "label",
    "y": "value",
    "yLabel": "Minutes later / more, 2017 vs 2016"
  },
  "dataset": null,
  "ranking": null,
  "related": [
    "https://karelbusta.dev/data/sleep/latest-bedtime-at-20",
    "https://karelbusta.dev/data/sleep/kids-told-to-sleep-more-for-100-years",
    "https://karelbusta.dev/data/sleep/sleep-duration-has-not-declined",
    "https://karelbusta.dev/data/sleep/dst-spring-fatal-crashes"
  ]
}