Do final year of high school in America?

I am currently doing the British GCSE curriculum in a foreign country. Junior year (11th) right now.
Also, I’m a green card holder and I have the chance to make the move to the US this year.
I will be applying to college in the US for fall 2016, meaning I have to finish my final year of high school.
If I move to the US, I will have to change my curriculum immediately to the American system and
do my AP tests that year itself. I think it will be a huge hurdle since I will be be studying a completely new curriculum, and have to do the main exams in that year itself, besides the fact I will be in a new environment in a school, and will have to adapt.

Is it a better idea for me to finish my final year of high school in my current curriculum, or make the move and do senior year in an American high school?

Part of the issue is the green card. You and your parents need to speak with a good immigration lawyer who knows the details for people from your country of citizenship. South American friends were told that they should spend less than 6 months outside the US on each trip out of the US.

Will you finish your A levels in one more year?

How soon is your family moving to the US? For family unity, it may make more sense in the long run if you move to the US with them now. Getting used to a new culture is challenging. You might like doing that at the same time as your family instead of a year (or more) later. If you are going to an area that a lot of people move to, you won’t be the only “new” student at that high school.

The “main exams” in the US aren’t the same as the exams in the GCSE curriculum. Some states have mandated graduation exams, but most are written for a 10th grade level. Except for American History, the subject matter probably won’t be difficult for you at all. In any case, the material is covered in class, and no one does prep for them outside of the regular school homework. Here is one list. Check the state where your family will be living: http://en.wikipedia.org/wiki/List_of_exit_examinations_in_the_United_States

If you plan to take the ACT or SAT, it will be easier to get help preparing for those in the US.

If you want to, and can, move as soon as possible.

Isn’t a better idea to first finish high school properly, in the same curriculum?

I will be finishing my A levels in spring of 2016. I’ve already done my SATs, so that’s not a problem. What I think is the problem, is the change in curriculum? Will it be a pain to get used to, especially in my final year?

Adjusting to the American curriculum won’t be hard. Most Europeans find American high school classes (even APs) easier than the classes they took in Europe. AP exams themselves are optional and the scores are used primarily to get college credit for the class. (In the US “calculus” is considered a college class, not a high school class. If you take it in high school, you’re ahead of the game!) You don’t need to take or pass a single AP exam in order to graduate from high school or attend college.

The American curriculum is easy to transition to because the courses are self-contained. You won’t have a history course in your senior year that builds up on a history course from the junior year. There’s one year-long US history course that students have to take sometime during their high school career, and that’s it. Same for the science. One year of physics, one year of chemistry, one year of biology, taken in some order over the course of a high school career. (Advanced students may opt to take a second year of AP science in addition to the first year everyone has to take, but that too would typically introduce all concepts again from scratch.)

That aside, your final year of grades won’t matter for college admissions in the US. American college applications are submitted in the fall of your senior year and admission decisions are based on that. And admission offers are not conditional on senior year grades or final exam scores, unlike admission offers in the UK.

   How long have you been outside of the USA on your GC? The GC is no longer a travel document. 

In addition, if you complete GCSE’s, you’ll be in Year 11 but that’s 10th grade - which is really good for you, actually,as it gives you 11th grade to improve your American application with stellar grades in AP classes (choose the classes where you got A/A* at GCSE level), then 12th grade to apply to college and take a couple more classes.
Very few universities consider GCSE/IGCSE sufficient to enter college (ie., university) in the US, and none that I know of have financial aid.
Transitioning from GCSE to AP should be fairly easy but choose your “landing” school and state carefully if you can - graduating from HS in Texas, NYS, California, Michigan, etc., will qualify you for residency (ie., in-state admissions with in-state tuition) but not all states function like this.
Check that your green card is valid - I think that you can’t be away from the US for a long time and keep it.