The first five years of English secondary schooling used to be referred to (intuitively) as years one (in which pupils would have their eleventh birthday) to five (in which they would have their sixteenth). The last two years of schooling, which are non-compulsory, are generally referred to as the sixth form as a relic of this older numbering system. Over the years, there have been many changes in the English education system, and a new year-numbering system has been introduced, meaning that the "sixth form" is now years twelve and thirteen of English schooling (year one is now in infant school). The term and concept, however, are still in general use.
In some parts of the country, special "sixth form colleges" were introduced during the decades from 1960 onwards, recognising this as a particularly important phase of student life. A large proportion of English secondary schools no longer have an integral sixth form.
See also: School years (United Kingdom)