He cannot cite hard data, nothing at all quantifiable, but Selah High School principal Colton Monti is keenly attuned to the gradations of moods and levels of attentiveness among the students he serves. So, believe him when he makes this bold proclamation:

“I definitely think kids are more alert at 8:40 (a.m.) than 7:40.”

It sounds so obvious, right? Give high school students an extra hour of shut-eye and they’ll be better prepared, cognitively and behaviorally, to learn. It’s understandable, then, that Selah High students seem perkier on Mondays, when the school day begins at 8:40, than the rest of the week, when they must drag themselves out of bed for a 7:40 start time.

This, of course, raises the question of why school districts in the Yakima Valley and statewide do not choose to hold first period at that 8:30ish sweet spot. Only Selah and East Valley highs have late starts on Mondays; the rest of the area high schools begin between 7:45 and 8 a.m. daily. Much of the reason for the earlier start is logistical: to change would mean to adjust after-school sports schedules, bus route pickups, and address parental concerns about day-care arrangements.

“Our district has looked at this,” Monti told us. “We’re always looking for ways to improve learning outcomes.”

Pushing back the start of the school day should be a no-brainer, since common sense dictates that teen-agers’ brains are functioning much more efficiently after the fog of sleep has passed.

Now, common sense is backed by hard data. A study released last week by the University of Washington, which followed sleep patterns of students at Seattle high schools that had rolled back start times an hour, has shown that students getting even as little as 34 extra minutes of sleep exhibit improved grades, attendance and behavior.

The research reinforces previous studies detailing how insufficient sleep negatively affects student outcomes. The American Academy of Pediatrics is one of a number of health-care advocacy groups that endorses moving back the school day to 8:30 or later starts for high school and middle school students. Later start times, according to a review of literature published by the National Institutes of Health, “correspond to improved attendance, less tardiness, less falling asleep in class, better grades, and fewer motor vehicle crashes.”

In the fall of 2017, Seattle Public Schools adopted the later start times (from 7:50 to 8:45) after consulting studies and heeding recommendations from the Centers of Disease Control and Prevention. The thinking was that teens’ biological clocks are hardwired for them to stay awake later into the evening and, optimally, wake up later in the morning. Pre-8 a.m. start times cut off the crucial last 30 minute to an hour of sleep, which scientists say does make a difference. Since Seattle schools made the adjustment — and parents adjusted their schedules, as well — the experiment has gone smoothly.

If Yakima Valley districts take a close look at the University of Washington results examining improved student outcomes, they might be convinced to make the change.

Researchers, the spring before the time change, outfitted sophomores at two Seattle high school biology classes with activity monitors that tracked data on sleep and movement over a two-week period. The next fall, after the start times changed, researchers repeated the experiment.

The results, published last week in the journal Science Advances, showed that the teens gained 34 minutes of sleep per night — maybe that extra 26 minutes was spent playing Fortnite or texting — and scored 4.5 percent higher overall on grading. Tardies and first-period absences fell slightly, as well. All told, the students averaged 7 hours and 24 minutes of sleep per night after the switch, still below the 81/2 hours recommended for adolescents.

“To ask a teen to be up and alert at 7:30 a.m. is like asking an adult to be active and alert at 5:30 a.m.,” University of Washington lead author Horacio de la Iglesia told National Public Radio.

Granted, a causal link between improved grades and the later start time could not be established, but the correlation is promising. Numerous researchers have long established a link between attendance and grades, so showing up — and staying awake while in class — is key. And it’s widely known that chronic sleep deprivation adversely affects cognitive function.

Schools, however, have been slow to adopt later starts. Seattle is the largest school district in the nation to push back start times. The National Center for Educational Statistics reports that just 17 percent of the country’s secondary schools start at 8:30 or later — most of those schools in urban areas.

Provided that school districts in the Valley can figure out how to shift after-school activity schedules and morning and afternoon bus schedules — and get parents to agree to alter child-care and work schedules — they should move back start times so that teen students will be ready to learn, not to yawn, by the first-period bell.