We all remember high school mornings. We dragged ourselves from bed in the dark and rushed to catch the bus to make that morning bell. While this has long been the norm, advances in sleep science have shown that this early schedule is harmful for teens. Between 6 a.m. and 8 a.m., most teens are hitting their sleepiest hours; yet this is when school start times demand that they get up, sit at a desk, pay attention, learn, and take tests.

As sleep doctors, researchers, and parents, we are committed to our children’s safety, health, well-being, and education. Keeping the status quo is unacceptable and dangerous for our youth.

Lower Merion jump-started discussions on later start times when it brought in pediatric sleep expert Judith Owens in 2014, years after concerned parents first raised the issue. Seeing the writing on the wall regarding student health and learning, the Radnor district voted April 23 to delay Radnor High School’s start time. Lower Merion and other districts have not yet followed suit, and their timeline for implementation, if it happens at all, remains unclear.

This lack of urgency is worrisome. We have a national epidemic of sleep-deprived teens: 87% of high schoolers get too little sleep, according to the National Sleep Foundation.

Why are teens so sleep-deprived? While the current trend is to blame screens, homework, extracurriculars, poor habits, or laziness, biology is the real culprit.

Adolescent brains are programmed for later bedtimes. Most teens do not feel sleepy until after 11 p.m. So early bell times, like 7:30 a.m. for Lower Merion’s high schools, demand that teens arise before being fully-rested and while they are sleepiest. To get the recommended 8 to 10 hours of sleep, teens would have to fall asleep by 9 p.m., which is not just unrealistic. It’s also biologically impossible because their internal clocks dictate that they fall asleep and rise later than other age groups.

Unsurprisingly, in a 2015 survey, Lower Merion’s teens reported falling asleep in class. In many districts, teachers have concerns about administering exams during first period, when students are not functioning at their best. This phenomenon is so distinct that scientists call it “the first-period effect.”

Not only is this learning environment suboptimal, national data show that early bell times are killing teens through drowsy-driving crashes. Additionally, a review of almost 600,000 teens found that getting less than 8 hours of sleep increased their risk for committing suicide.

The evidence has been so compelling that in 2014, the American Academy of Pediatrics recommended start times no earlier than 8:30 a.m. for middle- and high-school students. Since then, numerous organizations, including the Centers for Disease Control and Prevention, American Academy of Sleep Medicine, and others, have added their voices to the growing chorus of experts insisting that districts delay school start times.

Terra Ziporyn Snider, cofounder and executive director of the national organization Start School Later, estimates that hundreds of districts around the country have responded to these recommendations. Research shows that those children are sleeping longer, having fewer car crashes, less suicidality, depression, and anxiety, and better school attendance and academic performance.

Any change in school schedules may pose logistical challenges. Transportation, after-school activities, child care, and sports must be coordinated and finances managed. As other districts have already proven, these obstacles are surmountable.

Until we unite in this shared vision, our students will continue to suffer. Procrastination and inaction cause harm. The safety and well-being of our children demands prompt action by those entrusted with their education.

We call on the Lower Merion School Board, and others throughout the Philadelphia region, to vote “yes” to delaying high school start times immediately.

All three authors are sleep medicine faculty in the University of Pennsylvania’s Perelman School of Medicine. Indira Gurubhagavatula, M.D. MPH, is a Clinical Associate Professor of Medicine in Penn’s Division of Sleep Medicine and chair of the American Academy of Sleep Medicine’s Public Safety Committee. Mathias Basner, MD, PhD, MSc is Associate Professor of Sleep and Chronobiology in Psychiatry. Dafna Ofer, MD, is Clinical Assistant Professor of Sleep Medicine and Pediatrics, and a mother of five children. The opinions expressed in this article do not represent those of the University of Pennsylvania Health System, or the Perelman School of Medicine at the University of Pennsylvania.