The phrase "sixth form" refers to the last two years of secondary education in some countries, usually from ages 16 to 18. It is a stage where students prepare for college or take exams before entering the workforce. Full definition
Students in sixth form colleges are already seeing increases in their class sizes. (politics.co.uk)
I enjoyed musical theatre all through school but stopped in sixth form as not enough time. (sport.ox.ac.uk)
The two - storey building was completed less than six months from receipt of order to be open in time for the school's first intake of sixth form students. (qaeducation.co.uk)