"upper secondary school" is correct and usable in written English. You can use it to refer to the last level of schooling before college, typically the equivalent of high school. For example, "The upper secondary school curriculum is very challenging.".
In the upper secondary school grades are given each term.
Nearly all of the pupils continue from comprehensive school to the upper secondary school.
As a result, the vocational sector was incorporated into the general upper secondary school.
Her mother had died while she was in upper secondary school and soon afterwards she lost her brother-in-law.
Applicants received between one and 100 points for the subject exams taken to earn upper-secondary school leaving diplomas.
The upper-secondary school system is selective, and students are streamed into different courses of study.
In Vietnam, students normally finish upper-secondary school at the age of 18 and enter universities at 19.
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