sixth form

Từ điển Oxford Advanced Learner 8th

ˈsixth form [sixth form] BrE NAmE noun usually singular (BrE)
the two final years at school for students between the ages of 16 and 18 who are preparing to take ↑A levels (= advanced level exams)
•Sue is in the sixth form now.

Culture:
The sixth form is often divided into the upper sixth (year 13) and lower sixth (year 12). Some students leave their secondary schools after taking the ↑GCSE examination and go to a sixth-form college, a separate school where students study for A level.