Eight years ago, when I wrote a book about life at Walt Whitman High School , I strongly supported delaying high school start times. Starting high school later, I argued, would improve teens’ sleep, health, driving safety and school performance. In fact, I pretty much supported this measure at all costs.

I have changed my mind.

Let me clarify. In June, the Montgomery County Board of Education will likely vote on a proposal to delay high school start times by 50 minutes, a necessary and overdue change. But to save on bus costs, Superintendent Joshua Starr’s plan would also extend the elementary school day by 30 minutes. I cannot support shifting high school hours if it comes at the expense of our youngest students and their teachers.

Finding a cost-effective solution to changing bell times isn’t easy. Starr appointed a work group that researched adolescent sleep patterns to formulate a thoughtful report. But it put so much effort into exploring high school issues that the effect on elementary schools appeared to be an afterthought. Starr proposed making a massive change to the elementary schedule without a plan for what to do with the extra time.

For transportation reasons, elementary schools operate on two tiers: 8:50 a.m. to 3:05 p.m. and 9:15 a.m. to 3:30 p.m. The new proposal would end school for the second tier at 4 p.m, which is problematic for many reasons. Sending kids home during rush hour lengthens their rides and further congests traffic; many children would not get off the bus until after 4:30, reducing their best chance for weekday unstructured playtime. Such playtime is “essential to healthy growth and development. To extend the school day when children ordinarily would be playing doesn’t make any developmental or educational sense,” said renowned child development professor David Elkind. “Research suggests that kids [with less unstructured playtime] are not as imaginative or creative as other children.”

In the winter, many Tier 2 students would arrive home after dusk, a major safety concern. And outdoor romps and reflection should not be relegated only to weekends and holidays. The crunched afternoon would also leave children less time to bond with family, develop friendships, participate in after-school activities and attend religious and cultural classes. Unless, that is, they stay awake later to squeeze these activities in before bed.

The work group summarized current sleep research regarding 13- to 25-year-olds. What about ages 5 to 10?

Sleep experts say that 5-to-10-year-olds’ bedtime should range from 7 to 8 p.m. They naturally awaken between 6 and 7:30 a.m. Starr’s proposed schedule would allot many children less than three hours to complete homework, play, eat dinner, bathe and read before an age-appropriate bedtime. “They really need between 10 and 12 hours of sleep. Where do you fit in family dinners?” said Jodi Mindell, associate director of the Sleep Disorder Center at Children’s Hospital of Philadelphia.

Forcing children with naturally early waking times to stay up later could afflict them with the same sleep problems that Starr hopes to prevent in teenagers. “If you restrict biological sleep requirements by half an hour a day, in a couple of weeks your child might be more irritable and less focused. Young children look like they have attentional problems when they’re sleepy,” said Helene Emsellem, medical director of the Center for Sleep & Wake Disorders in Chevy Chase.

In a memo to the school board, Starr rationalized that the extension is “a much needed addition to our instructional day that will allow time for learning opportunities for students.” That’s not necessarily true. It is well established that grade-schoolers learn best in the morning. At approximately 3 p.m., they can hit a circadian slump. “Kids aren’t going to learn anything. They’re pretty tired at that time,” Elkind said.

Studies have found that more school time does not automatically lead to more learning. U.S. school days are already longer than those in many countries that dominate international tests, including Finland, where students score highest in the world.

Children learn best not from extra hours but rather from great teachers, who need time for both classroom planning and a healthy work-life balance. Under Starr’s plan, teachers would remain at school for 30 more minutes. Would they be paid extra? Teachers already spend hours on their job outside the school day. Sending them home during rush hour could impact their personal and family time, increase commutes and dissuade excellent teachers from working at down-county schools.

Fortunately, it’s not necessary. The county can find funds for the extra buses necessary to meet the sleep needs of all students. In fiscal 2015, for example, the Board of Education earmarks $3 million for devices to “support the administration of new state assessments.” That money could be better used.

Starr rightly calls sleep deprivation a public health and safety issue, but this applies to all students — not just high-schoolers. A significant shift for younger children deserves at least as much consideration as that for teens.

Alexandra Robbins is the author of several books, including “The Geeks Shall Inherit the Earth” and “The Overachievers.”