One thing I know is that everyone’s sleep needs are different. In addition, regardless of a person’s unique minimum sleep requirements, if they get less than their personal need, they are grumpy, and resiliency drops. In one family I know the mom has only needed 6-7 hours of sleep whereas her husband and sons all need eight to ten hours of sleep (and at times even more).
As a teacher, I could see the children who came to school with enough sleep as they looked rested, they tended to be optimistic, better problem solvers, less reactionary, calm, focused, and productive. Children who came to school with dark circles under their eyes tended to be reactionary, quick to anger, less focused and less productive, struggled to think of solutions, were more fidgety, and unfortunately if one asked a few questions found out that the lack of sleep wasn’t always due to the lack of bedtime, but due to the disruptions by the adults in the household (loud noise, loud music, t.v., hunger and arguments).