(I thought I could just edit my last post with another comment, but it turns out I have a lot more to say)
A lot of schools in Europe seem to have multiple "streams" of education during highschool, dividing students based on aptitude at a fairly early age (14 or so, though my school in Canada pretty much did the same, with two classes for each main subject, one academic, one not so much). I like what you said Abi about mixing all the students for the first year then dividing them after that. That could be really interesting in a fic.
I might further question, do students have the opportunity to switch classes/levels and if so, when? Do they have other exams besides the OWLS and the NEWTS?
I've looked up the acronyms used in the French translations of the books on wikipedia :P and on the Encyclopédie Harry Potter (link goes to the ASPIC article if you speak any French, the site might be a useful too, but then I'm never sure how welcome introduction of a second language in fiction is.) In any case:
OWLS are: (les) BUSE (Brevet Universel de Sorcellerie Elémentaire)
NEWTS are: (les) ASPIC, (Accumulation de Sorcellerie Particulièrement Intensive et Contraignante)
From what I understand, the OWLS and the NEWTS are pretty standard across the wizarding world, so the subjects would probably be the same all over, as would the evaluation methods.
Maybe they take their OWLS at the beginning of their 6th year? Maybe NEWTS are optional? Maybe NEWTS are taken during the summer after graduation so as to give more time for preparation, allowing Beauxbatons to boost their scores and look better in the wizarding community :P