For one, our schools start too early. Despite a plethora of studies that show that middle and high school students benefit the most from late starts to the school day, we continue to force students to be to school before 8am (let alone the recommended 9am). Even college age students do their best to avoid 8am classes. Yet we have some students who, due to practice schedules, actually have to be at the school by 6:30am. When you add in hours of homework, after school activities going throughout the evening, and television studios putting their most attractive (to high school age students) shows after 9pm, it is no surprise that many students are yawning through their school day.
To make matters worse, we throw too many subjects to them through the school day. A full load at the college is between 12-18 credits (with 18 pushing the limit). That's the equivalent of three to six classes a semester that meet between one to four times a week. Most high schools run a six-class schedule, with students having to juggle the maximum subjects of most college schedules while meeting for five hours a week for each subject. Despite what many politicians claim, our students are actually in school too long.
We also need more selection for our students. Right now they are packed into classes that supposedly teach the same standards at the same time even though we know that students learn differently and at different paces, and even though we know that not all of our students will need the exact same lesson at the same time.
Later starts and a varied class system with fewer on ground hours is a program that has made our colleges and universities some of the best in the world. I know that we would still need to supervise our students through the school day (something that colleges don't need to worry as much about), but we could do so by allowing students to pick tutoring centers during the time that they are not in direct instruction classrooms. These centers could range from study halls that provide a quite place to work, recess areas to give some of our students that much needed activity that they are often denied, "reruns" of courses so they get a double hit of the info, student-led group study sessions, or even one-on-one tutoring.
There are flaws with my proposed system, but I think that it's better than most schools are doing right now. Granted, any system is going to do poorly under the current financial and legislative constraints that public schools are currently under. Still, it's nice to dream.