Students who graduate from a US curriculum High School will do so with a High School Diploma, which is a reflection the 14 years of work proceeding it.
Historically, every US State had its own curriculum standards, and, therefore, the academic quality of the High School Diploma was at best variable! Over the years, changes have been made not only in terms of a common set of standards being put in place by the US Government - the US Common Core Standards - which apply only to English Language Arts and Math, but Associations of Schools and Colleges, representing geographic areas of the US have been formed to provide accreditation for their members, as a means of guaranteeing the quality of the curriculum provided.
Today, there are four Associations - NEASC, MSA, WASC and Cognia - that are the accreditation organisations who work with schools both within the USA and internationally to ensure that the quality of education delivered will be recognised by colleges and universities in the US. Students who attend a US curriculum school overseas should ensure that their school is accredited with one of these associations in order to be certain that their High School Diploma will be recognised.
Having a high school diploma is essential for university entrance, but in some ways also irrelevant. Getting into US university is not based on a final grade at high school. Rather US universities take a distinctly less academic view, looking at your profile as a whole: The number of courses you have taken (how academically interested are you), how you're expected to do in those courses (US universities will offer you a place before you sit your final exams), and your extra curricular activities (what are you going to contribute to college life, not just your course).
The US is also less focused on what you have studied. To some degree this reflects the fact that you don’t usually decide what your main focus at a US college until the end of your second year. In the UK, and Europe as a whole, you focus almost immediately on one subject.
Finally, perhaps the "real" exam or pass you are looking for for for US universities is not the US high school diploma, but your SAT, or “Scholastic Assessment Test” or ACT, "American College Test". These are compulsory tests, and determine your abilities in writing, mathematics and “critical reading” or reasoning.
In other words your high school diploma matters only in as much it reflects what you have done with your time at school, which in turn will reflect how a university sees you as a human being. It will be one facet of what a college will be looking for.
This for example is what Columbia University says matters:
Criteria to actually obtain your high school diploma will vary from state to state - one of the reasons why talking about a "US education" or curriculum is difficult. It will require at a minimum the continued study of core subjects and a minimum grade point average.
Note: Academically gifted students at US high schools will also look to take Advanced Placement (AP) exams. Again, how well you do at these exams will not determine your success or otherwise in university admission. It will however send a statement regarding how much you challenge yourself academically, your intellectual ambition, and perhaps your overall potential. Students capable of doing well at the AP exam will also take it because it will give you college credit.
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