Why are some secondary/sixth form schools called “4-18” while others are called “4-19”?

[lindaandrews]

This is for a school that has a nursery, primary, secondary and sixth form but one for some reason doesn’t include 19 year olds and another does.

Most people will do 2 years for A-levels but the government funds 3. I did my A-levels over 3 years instead of 2 as I had a complete change of direction. The first year I did languages, have AS-levels in those, then 17-19 I did sciences and have full A-levels in those.