The issue has existed since well before widespread availability of smartphones and cheap laptops. Here's a clinical review from 2003 (largely citing studies fr

The issue has existed since well before widespread availability of smartphones and cheap laptops. Here's a clinical review from 2003 (largely citing studies from the late 1990s) where the same issues were already clear: http://web.mit.edu/writing/2010/July/Wolfson%26Carskadon2003.pdf http://web.mit.edu/writing/2010/July/Wolfson%26Carskadon2003... One major part of the problem is that teens tend to go to bed at the same time regardless of when school starts the next day. Hence those students in school districts with earlier start times simply get less sleep, resulting in more irregular sleep schedules. In turn, that leads to worse cognitive performance.