Teens learn better if allowed to sleep longer:

This paper uses data on all middle school students in Wake County, NC from 1999-2006 to study the impact of start times on academic performance. … The differences in start time across schools is generated by bus scheduling concerns, while the differences within schools are driven by population growth. … I find that a one hour later start time increases standardized test scores on both math and reading test by three percentile points. Since start times may be correlated with other determinants of test scores, I also estimate the effect using only variation in start times within schools over time and find a two percentile point improvement. The effect of start times on academic performance is robust to different specifications and sources of variation. The magnitude of the effect is similar to the difference in test scores for one additional year of parental education.

The impact of later start times on test scores is persistent. Conditional on a high school fixed effect, a one hour later start time in grade eight is associated with an increase in test scores in grade ten similar in magnitude to the increase in grade eight. … The impact of start times is greatest in grade eight (who are more likely to have begun puberty than those in the sixth or seventh grade). … Students who begin school later have fewer absences and spend more time on homework each week. … Over the seven years examined in this paper, [this school district] grew from 20,530 student enrolled in twenty-two middle schools … to 27,686 students enrolled in twenty-eight middle schools. (more)

Do you predict that once news of this study spreads, schools will all delay their start times?  Me neither.

So why do we insist on getting teens up early, if that hinders learning? For the same reason we test and rank students so often, even though that also hinders learning. School isn’t about learning the content of classes – its more about socializing humans to accept industrial workplace norms and practices.