At the end of primary school (your elementary) we can choose to take an exam called the "11+". So the people in yr6 are 11 or slightly older. The exam decides on whether you go to a comprehensive school or a grammar school (I'm not sure how private schools work; lots of money as well as the exam I think.)
Also, in many cases our schools are all fused into one. My grammar school taught kids from 11 to 18, which is the equivalent of your middle, junior-high and high schools. Also, grammar schools tend to be single-sex.
Here's a list of what I did in yr7;
English, Maths, French, History, Geography, Computing, Latin, Biology, Chemistry, Physics, Technology, Music, Art, PE (gymnastics etc), Games (field sports), and RE (a legal requirement now).
And yes, there are uniforms, latin slogans, school songs, ...