I barely remember anything from High School. I mainly just remember the things I learned in Science related classes, Physics, Biology, etc... Aside from that, World History. Those were my favorite subjects so I never really let that info slip from my memory.
I'd say English Composition too, but to be honest I've become a better writer while in College than I was back in Highschool. I think that is due in large to Highschool writing being approached like it has a prescribed format. I was taught there was a basic template every essay should follow. The opening paragraph should be shaped intellectually like an inverted pyramid. Start broad, then narrow down to a specific thesis. Three paragraphs afterward should support the thesis. Each of those paragraphs should start with a thesis sentence. The conclusion would be shaped like an upright pyramid, starting with a specific point and then expanding out, and ending with a broad concluding statement that opens up what the essay implies. 12 years of grade school and I left thinking writing is formulaic, and I think everyone probably left Highschool thinking the same thing, atleast if they are from America.