>>6 Double Science

Is that like the "Double Potions" class in Harry Potter?

In fact, could someone please explain the entire British educational system in terms of Harry Potter? Like, I've sort of figured out that the "O-levels" are like the O.W.L.s and the "A-levels" are like the N.E.W.T.s, is that right? How does the rest of it work out? How are the students sorted into houses at real schools? Are the houses equivalent? Like, was Suede in a Hufflepuff-equivalent and Cracky in a Slytherin-equivalent, or are the houses IRL completely different?