There's been a sharp increase in the number of British students attending American colleges in the past decade. As well as it being a completely different education system, there are other surprises prospective applicants might want to consider:
College and University - You can obtain an Undergraduate or Bachelor's degree from institutions bearing either title. Universities typically offer undergraduate and graduate degrees, while some colleges only offer two-year, associate degrees. This is not set in stone however. Harvard College is the undergraduate arm of the larger Harvard University but Boston College is not part of Boston University, and offers undergrad, graduate and doctoral degrees. Most people talk about a "college degree" rather than a "university degree" and use the generic term "college" more than "university" when talking about higher education. (The term "college" is used here throughout.)
School - Americans often mean college or university when they ask "Where did you go to school?" If they want to know anything about your prior education, they will typically say "high school".
There is no UCAS equivalent. In general, you apply to individual colleges, although there is the Common App (Application) which allows you to submit the same information to several colleges at once. Not all institutions use the Common App and even those that do, often still require an individual essay or five, specific to their courses. For this reason, applying to American universities is more time-consuming than the British equivalent. Oh, and they don't all have the same deadline.
Some colleges are in the middle of nowhere. You might think there are remote parts of the UK, but try being a hundred miles from the nearest airport. As an international student, perhaps the last thing you need after a nine hour flight is a four hour bus drive to campus. In addition, although the colleges are usually situated in a small "college town", if there's no bus service and you don't have a car, you're at the mercy of your driving friends or you're stuck in one place.
An undergraduate degree usually takes four years - an important factor when considering the cost and your threshold for academia. In some cases your super-duper A level results can get you credit, which acts as "time off for good behavior" and allows you to graduate early. This is also important when considering costs as it's almost a pay-as-you-go system.
You can't drink till you're twenty one - Although American colleges differ in their approach to under-age drinking, it is illegal in all fifty states and your involvement might lead to police activity rather than just a slap on the wrist from the Student Affairs office. Additionally, your errant ways can end up on your college record, result in fines and restrictions on campus, or even get you kicked out. (And remember, getting kicked out of college means you're out of visa status and at risk of deportation.)
Most students share a room. - Yes! Even though you're an adult, the majority of dorm rooms house two or more students. Many colleges have single rooms if you hate the thought of strangers snoring less than four feet from your head, and as you'd imagine, those rooms go fast. Some colleges mandate that freshmen (first year students) live on campus.
The weather in the USA varies wildly.- If you attend a northern college, the winters can be brutal. Temperatures in states like Minnesota can stay below freezing for three or four months, which severely curtails outside activity. If you attend a southern college the heat and/or humidity can be hard to bear, although you may not be there in the summer, when it's at its fiercest.
Visas. - Unless you have dual nationality, you'll require a student visa but there's no point in worrying about that until you have applied, received an offer and formally accepted it. Only the college that you will attend can kick start the visa application process so save the worrying for something like A levels.
The fees at American colleges can be eye-watering. - According to the College Board, the average yearly tuition for international students in 2015-16 was $32,405 at private institutions and $23, 893 at public ones. (I would insert the sterling equivalent here but it's ever-changing.) Bear in mind that's an average; some of the "big name" colleges are much higher. In the same period, tuition at Harvard was $45,278 and $60,659 all-in (ie. tuition, room and board). The good news is that there is financial aid to be found. Many colleges have funds to help students meet the costs, and while the bulk goes to American students, many international students receive assistance too. My recently-graduated daughter had a circle of friends that resembled the United Nations and the majority received some form of financial assistance.
You can get the low down on thousands of American colleges at web sites like http://www.studentsreview.com/