I study at Oswestry School on the A-level program. To be brief - this is a special course to prepare for admission to a foreign university (they do not directly accept after the graduation from the Russian school). I arrived in England two years ago, finished middle classes here, and then I entered the A-level.
There was no language barrier, I've been learning English for a very long time, but even now sometimes there are difficulties with academic, scientific terms: the A-level course is considered to be complex, in-depth (like the first year of the university), because here it is not just "London is a capital of Great Britain "). The teachers help very much. You can always come up after the lesson, take a separate individual lesson (by the way, free consultations are almost always available), there are courses for those who are more difficult to give a language (such as supporting additional lessons, but I'm already allowed and not to visit them constantly). In general, I will say that it is difficult to study, but if they see your desire, they will do everything to help you.
My school is very calm, rural boarding type. In fact, this is super-convenient, when both study and housing in one place - do not bother, how to get home and how much time to spend on the road: five minutes - and you're already in the hostel. And of course, this is not at all the "hostel" to which we are accustomed in Russia: it is rather such a cozy student hostel in Europe - everything is brand new, beautiful, comfortable. In order not to get bored in the same place and not feel like a "prisoner of a boarding house", you can always make an appointment for a tour or a trip, even a walk around the neighborhood, even to London. True, I myself do not go very much - the time is spent for studying the sea, I go out with my classmates to drive a ball or play tennis, and everything, in general, but many people like to drive.
I hope that my efforts will pay off - the main thing is to pass the A-level exams on a high score, and then the doors of any university, even Oxford, will be open to you.