"When teens want to sleep in on a school day theyre not being lazy. For one teens need more sleep than adults about eight or nine hours a night compared with about the six or seven their parents require. Teens biologically really do crave sleep.  Which is a problem when it comes to education. Most high schools start before  am http to help parents get to work by  am. Early school start times also give kids more time for afterschool activities like sports or theater.  But that has consequences Around  percent of high school students get less than eight hours of sleep on a school night according to https the Centers for Disease Control and Prevention which puts these teens at risk of negative impacts on health. There may be a simple fix Start schools at a later time.  This is a solution supported httppediatrics.aappublications.orgcontentpediatricsearlypeds..full.pdf by both the America Medical Association https and the American Academy of Pediatrics httppediatrics.aappublications.orgcontentpediatricsearlypeds..full.pdf. The AMA urges schools to start no earlier  https  am. In  the Academy of Pediatrics wrote that the urgency and the magnitude of the problem of sleep loss in adolescents warranted big changes in school start times.  But its not a foregone conclusion that later start times will ensure teens sleep more. Later start times could lead teens to go to bed even later. Or parents might still wake them up early. When it made its recommendation the Academy of Pediatrics admitted it is clear that additional research is needed to further document the effects of changes in school start times over time. Well theres some new but still incomplete evidence that later start times do help teens get more sleep. A new metaanalysis http in the Journal of Clinical Sleep Medicine analyzed  studies on start times. It finds that when school starts up to an hour later students typically do get around  minutes more sleep on average. When start times are delayed more than an hour that average increases to  minutes of extra sleep.  The study also found some preliminary evidence that later school start times were associated with better mental health outcomes. Only five of the  studies included these measures but in two of them later start time was associated with better selfreported feelings of depression and irritability.  More work needs to be done to confirm these findings. But even if later school start times only improve sleep time thats a positive step for public health. Because if later school start times can truly help students sleep better the research suggests that better sleep would lead to major improvements to their health and wellbeing.  Teens tend to be night owls and forcing them to be early birds can mess with their health  Teens tend to go to sleep a bit later and wake up a bit later than the average adult  something called a delayed sleep phase. For most teens it means their whole biological clock is shifted and if they wake up too early their body will be out of sync with the rest of the world. Every neurotransmitter hormone and chemical in the body cycles with the daily rhythm Philip Gehrman a sleep researcher and clinician at the University of Pennsylvania told me http earlier in the year.  When your body clock is off from societys scientists call it social jet lag. And like the jet lag from a long journey it messes with your body.  Studies of adults find that social jet lag is associated with higher BMI insulin resistance http depression and a higher likelihood to engage in dangerous behaviors like smoking. And the group of people most at risk for social jet lag Teens.  In a tightly controlled lab study  healthy adult participants who had their sleep shifted by one hour each day simulating jet lag started to look prediabetic http after a threeweek trial. Their resting metabolic rates dropped  percent. Assuming no changes in activity or food intake that would translate into . pounds increase in weight over a single year the study published in Science Translational Medicine in  concluded http People with a lot of social jet lag also tend to get fewer hours of sleep which exacerbates these same health problems. On top of that short sleep reduces powers httphealthysleep.med.harvard.eduhealthymattersconsequences of perception concentration and judgment. Theres some evidence http that when students sleep better they perform better in school as well. A lot of the studies on social jet lag and short sleep use adults as their participants. But as the American Academy of Pediatrics reports httppediatrics.aappublications.orgcontentpediatricsearlypeds..full.pdf studies do also find an association between short sleep and obesity in adolescents. Delaying school start times is easier said than done As Voxs Libby Nelson has reported http very few schools have actually adopted this reform. This map which reflects the most recent CDC data available shows that across the country schools still start very early.  There are some understandable reasons why. Nelson writes http  ...the problem is usually logistics. Students of all ages usually share the same fleet of buses. High school students get the first shift and the buses circle back to pick up their younger siblings later in the morning. Most districts dont want elementary school students to have to wait in the dark for buses early in the morning  nor do they want to pay for a separate fleet of school buses for elementary and middle school kids. Breaking with tradition turns out to be costly. And even though the evidence is mostly in favor of increasing school start times it isnt a slam dunk quite yet.  There are some limitations to mention about the new metaanalysis. The studies mostly used selfreported measures of sleep duration. More objective measures  like those obtained from Fitbitlike wristbands  are more accurate. And many of the studies were short in duration comparing sleep duration in snapshots before and after a school made a switch. More data would show whether the impact of school start time on sleep waned or improved over time. The aggregated quality of the evidence the study reports is only moderate. The researchers also found no effect on academic performance. Furthermore two of the studies found evidence that earlier start times were associated with increased vehicle accidents involving the teens. Being tired in the morning can be a dangerous distraction while on the road.  In all the researchers call for more rigorous data on the topic. As schools change their start times they write researchers should sweep in to collect information on students sleep in a standardized way. Regardless its a promising area for study. Because if later school start times can truly help students sleep better the research suggests that better sleep would lead to major improvements to their health and wellbeing."