In the independent school world, few students get anything like the nine hours of sleep recommended for optimal adolescent functioning. For the 15,260 independent school students surveyed by the Independent School Health Check, only 8.3% reported more than 8 hours of sleep the night before; 9.9% reported less than 5 hours sleep. Overall, 64.2% got less than 7 hours sleep. One consequence of such sleep deficits may show up as mood disruptions, as reflected in the table below that pairs sleep hours with responses to mood questions.
To the extent that staying up late is in the service of studying, students may accept tiredness and bad moods as the price they pay for better grades. An article in the August issue of Child Development calls that premise in question in its conclusion that: “Although we expected that nights of extra studying might not be as effective as students suppose (Pilcher & Walters, 1997), it was somewhat surprising that nights of extra studying would be associated with worse academic functioning the following day. This surprising finding, however, made more sense once we examined extra studying in the context of adolescents’ sleep. “
 Gillen-O’Neel, C., Huynh, V. W. and Fuligni, A. J. (2012), To Study or to Sleep? The Academic Costs of Extra Studying at the Expense of Sleep. Child Development. doi: 10.1111/j.1467-8624.2012.01834.x