Sixth formers

In the education systems of England, Northern Ireland, Wales and some other Commonwealth countries, sixth form (sometimes referred to as Key Stage 5) represents the final 1-3 years of secondary education (high school), where students (typically between 16 and 18 years of age) prepare for their A-level (or equivalent) examinations.

The term sixth form describes the school years numbered 12 and 13, which are called the Lower Sixth (L6) and Upper Sixth (U6) by many schools.

The term survives from an earlier system when the first five years of English secondary schooling were known as forms (which would originally have been long backless benches on which rows of pupils sat in the classroom). Pupils started their first year of secondary school in the first form or first year, and this was the academic year in which pupils would normally become 12 years of age. Pupils would move up a form each year before entering the fifth form in the academic year in which they would have their sixteenth birthday. Those who stayed on at school to study for A-levels moved up into the sixth form, which was divided into the Lower Sixth and the Upper Sixth. In some private schools, the term Middle Sixth was used in place of Upper Sixth, with the latter being used for those who stayed on for an extra term to take the entrance examinations that were previously set for candidates to Oxford or Cambridge universities. Other schools described these Oxbridge examination students as being in the Seventh Form or Third Year Sixth.

The system was changed for the 1990–1991 academic year and school years are now numbered consecutively from primary school onwards. Year 1 is the first year of primary school after Reception. The first year of secondary school (the old first form) is now known as Year 7. The Lower Sixth is now Year 12 and the Upper Sixth is Year 13. However, the term "Sixth Form" has still been retained as a vestige of the old system and is used as a collective term for Years 12 and 13. Public (fee-charging) schools, along with some state schools, tend to use the old system of numbering.

...
Wikipedia