An All-through school is a school which provides both primary and secondary education. In the United Kingdom, they accept children at age 4, and school them right through to the age of 16 (or 18 with a sixth form).
In 2009, there were only 13 all-through state schools in England, but the Coalition Government's Free school (England) programme has seen the number expand rapidly.
Definition
The term "all-through" can be legitimately applied to establishments in many different circumstances, but one commonly accepted definition is "schools which include at least two stages of a young person‟s education within the one establishment".
References
All-through school Wikipedia(Text) CC BY-SA