By Henry Nicholls

In 2014, the American Academy of Pediatrics recommended that middle and high schools start no earlier than 8:30 a.m., a policy now backed by the American Medical Association, the C.D.C. and many other health organizations.

Whenever schools have managed the transition to a later start time, students get more sleep, attendance goes up, grades improve and there is a significant reduction in car accidents. The RAND Corporation estimated that opening school doors after 8:30 a.m. would contribute at least $83 billion to the national economy within a decade through improved educational outcomes and reduced car crash rates. The Brookings Institution calculates that later school start times would lead to an average increase in lifetime earningsof $17,500.

Since 2014, several states have passed legislation related to school start times. In August, California lawmakers passed a bill that would have gone further. By 2021, most middle and high schools across the state would have had to start at 8:30 a.m. or later.

It was landmark legislation, according to Terra Ziporyn Snider of the grass-roots organization Start School Later, which has been campaigning for change since 2011. “It is becoming less acceptable to run schools at unhealthy hours, and this bill reflects that sentiment,” she said. But California’s governor, Jerry Brown, vetoed the bill on Thursday amid opposition from local officials, a deeply regrettable decision. It shows a tragic disregard for both the mental health of children and for science.

But Ms. Ziporyn Snider remains upbeat: “Eventually a bill like this, created in the best interests of children, will pass. It’s only a matter of time.”

Parents need to be vocal about the reasons change is so important, joining forces with community leaders, sleep scientists, health professionals and educators to put school start times on the local, then state agendas.

Changing the operating hours of an institution so central to the community is far from easy. It requires strong leadership and adjustments by school bus companies and businesses offering services like child care and extracurricular clubs. But despite the upheaval involved, making such a shift would pay off in the long run. It is unthinkable that a school should operate with asbestos in the ceilings, with no central heating in winter or with rats in the kitchen. Starting school before 8:30 a.m. should be equally unacceptable.

Henry Nicholls (@WayOfThePanda) is a journalist, science teacher, trustee of Narcolepsy U.K. and the author of “Sleepyhead: The Neuroscience of a Good Night’s Rest.”