When I can't sleep, I try to hash out things in my past. If favorite rumination correlates well with amount of time spent on it, then my education is currently my favorite pillow thinking.
High School science is straightforward from a teaching perspective. You start with Biology, with subjects like bones, arteries, and lungs, which kids can readily apprehend by looking at themselves. But in Biology, you do have to memorize stuff like ATP = Adenosine TriPhosphate, which has to do with an energy cycle, but you have no idea how that works, it just does. Luckily, the next year, you take Chemistry, which explains that ATP is a molecule with bindings between the atoms, some of these bonds when broken release a significant amount of energy. You see that the breaking out of ATP's phosphate groups yield the most energy. But what is energy anyway? Then you take Physics, and you finally learn about energy in its various forms and that matter and energy are interrelated.
The first three years of high school science classes take the student from what they can readily grasp by direct observation to fundamental elements of the world around them. But then, in your senior year, this path is complete and the student can take an advanced class in either Biology, Chemistry, or Physics. It would be interesting to offer a senior-level class that worked from Physics upwards to Chemistry and Biology, allowing students to explore the bindings between the divisions in science, or to do advanced work in any of the divisions. This would help re-inforce the idea that ideas from disciplines bleed into other disciplines, in addition to helping students answer why things work, no matter the division of science.
History, on the other hand, starts with the remote idea of "no one writes anything down" pre-history and works its way forward. Although the founding idea is foreign, it is a base, and the teacher can show developments over time as growth (or not) from this base. So you learn dates of events in order to be able to correlate and compare different developments from that base. In my high school, I learned history as a series of tensions that lead to conflicts. The Serbian nationalist Gavrilo Princip picks up a pistol and assassinates Archduke Franz Ferdinand and we end up with World War I. Well, aside from whatever was going through Gavrilo's mind, there are the ideas of Serbian Independence and Entangling Alliances. This is all well and good, but it is only after several years of study of history that students get to the current time, which is the only place that they can observe directly.
Since students are living in the now, it would be interesting to help students answer "why are things the way they are today?" by teaching a senior year history seminar that runs time backwards. Students can work from the immediate now and its apparent trends to why those trends are in place. And keep on walking backwards until they get to the base of pre-history.
English suffers the most of the disciplines, as its only common development thread is that of mounting complexity in the material. As such, there is considerable freedom in what is presented to the students. For example, my senior year English class served as proxy for Psychology 101. The difficulty lies in that there is no overarching plan that the student can strive to determine. The best that I could see was that my teachers had vastly different preferences in what was "good", and that their "good" was positively correlated to how difficult it was for me to recreate.
Because English is so open, it should be student-directed. Teachers should act as good librarians, recommending increasing difficult texts for students to read given the students' interests, while requiring them to write analytical papers, create works of their own, and present their ideas to the class.
Running almost completely opposite to English is Math, as Mathematics is fundamental to Mathematics. Students are boot-strapped into higher maths year after year, with Calculus providing an inclusive bundling of all prior maths. As such, the ordering of maths is fairly well set with maybe some dickering over whether Geometry or Algebra goes first. But, many students are turned off from math. In my high school, we did not apply math until our junior year with Pre-Calculus and Physics. By that time, many kids had been lost.
Mathematics, if not applied, has no immediacy for a student. Which is why we hear, "When am I going to use that in real life?". Combine Geometry with wood-work, origami, knot-tying, etc.. We should combine Algebra with solving business problems that a teenager runs into in real life, with problems from biology, or the other classes the student is taking. Make the problem immediate for the student, and the student will seek to find a solution, learning as they go.
These changes may or may not take place. They are merely my observations about what I would have done differently. High school administrations have the demands of the state, parents, colleges, and businesses to worry about. Perhaps primary and secondary education will continue as as before, but there are some interesting changes afoot.
In a few years, schools are going to have to cope with a rise in the number of children coming to school after multiple years of LeapFrog learning. Education via LeapFrog is completely self-directed, the child picks up the LeapPad whenever they want to, loads the cartridge they want to, and uses it for as long as they want to. Contrast this with your primary and secondary education. Teachers are going to have a difficult time meeting LeapFrog-aided children's educational expectations; teachers are less interactive, sometimes too fast, sometimes too slow, sometimes talking about dumb stuff. LeapFrog students will score well on achievement tests, but their attention in class will be less than historically normal. Disaffected self-directed learners have always posed problems for the modern educational process, but they have been an ignorable minority. LeapFrog is poised to create a majority out of the Disaffected Self-Directed.