Hmm, the vexed question of native speakers, eh? The following may be a bit rambly, and I apologise in advance.
I was lurking on an interesting discussion of this on an MFL teachers' forum a few months back, actually. There was a wide range of opinions, but there was a broad consensus (even for the teachers who were fed up of high mark boundaries), that they would not be able to run A-level MFL courses without native speakers, due to low class numbers otherwise. Although it wasn't mentioned, I expect the presence of native speakers (who bump up the average grade and balance out students who cannot make the jump from GCSE) is very helpful when management analyse the statistics after results day, looking for courses to cancel altogether. Everything is about Bleeping Results Tables, remember!
My anecdotal experience bears this out. Every extra classmate really counts!
In terms of A-levels, A-level first language and A-level second language has the potential to work. Hypothetically. However, we only have that for Welsh,
a) because it is actually a traditional native language on this island
b) because, more importantly, many Welsh people campaigned like hell to get their own language recognised after centuries of English suppression and oppression!
First-language A-level German, French, Spanish, Italian, Dutch, etc courses would never run, even if they were introduced. Which they absolutely never will be.
The other thing, of course, is: what are A-levels for? If we assume that their only function is as elite entrance tests for university, then perhaps we should be blocking native speakers. But are they?
I admit that is their main use, but people take them for other reasons. An A-level certifies that you have reached a certain level of knowledge. People study for: the learning experience itself; for their CV, regardless of whether they plan to go to university. The native speaker has just as much of a need for a reputable, easily-understood certificate proving they can speak a language when they apply for a job as anyone else.
If we did decide that we wanted to block native speakers from A-levels, how would we do it? Whom would we block?
It can't be done by birth certificate. (There was a nice lady in my GCSE class who was born in Germany, and hardly knew any German!) We'd have to do a pre-A-level test of knowledge, but... It's easy to deliberately fail any exam. I can fail exams standing on my head! Wouldn't it be easier to simply reform the whole cohort-referencing system?
But, for the moment, let's assume we can magically sieve applicants out. Where do we set the bar? People who have an unfair advantage, presumably? Where's that, though? Some children with a qualified MFL teacher parent have more of an advantage than some English/English-born children with a native speaker parent.
I had a classmate who was:
a) one of those irritating creatures known as a natural linguist!
b) had spent a good part of childhood in Germany; and
c) had spent a good part of adult life in Germany.
Unfair advantage, yes? I thought they were guaranteed an A/A* to start with! Their German was lovely to listen to. This person scared one grade higher than me on GCSE- I got an A, because my speaking and listening pulled me down, and they got an A*. On AS German (which wouldn't have run if that person hadn't been there) we got the same overall score. Grade D each. Theirs was a C in speaking + E on the paper, and mine was an E on the speaking and a C on the paper! They just didn't hit the high mark bands on the speaking.
But I guarantee this person would pass the Goethe B2 tests with ease, despite that. Possibly the C1 ones, too.
The other native or nativish Germans over the last couple of years have been getting grades between C and A. Nothing to sneeze at, but they've not been dossing their way to that, either. Native speakers can write terrible essays; they can have bad grammar; they can simply not meet the top criteria for content; they can have sodding awful exam technique.