Several years ago I was in a meeting at school. It was probably a department chairs meeting but it could have been a faculty meeting - I'm not sure. But the topic of discussion was the length of the school day. Several people wanted to make it longer. More teaching time and perhaps more time between periods so that students would not be out of breath when they arrived at classes after moving the lenght of the building.
No one disagreed that longer days would be a good idea. The point of contention was should the day be made longer by starting earlier or ending later. Seems simple doesn't it? But it is not.
The down side of starting earlier is that high school students don't function very well early in the morning. Some of it is a function of them staying up too late working, playing or doing what ever else young people do. But part of it is that this is just the way teens bodies work. Younger children work better earlier; teens later. You may notice that most school districts start high school earlier in the day than elementary school even though the research pretty much suggests the other way around would be better. It's not about the kids - it's about what is easier for parents.
So if starting earlier is not a good idea educationally what about ending later? Easy right? Well not quite. You see if school ends later it causes all sorts of programs for sports teams, especially those who compete outdoors. We can't have that now can we?
And that dear readers is why the school day is too short.