http://en.wikipedia.org/wiki/Educational_stage

Age	Education	2 stage	3 stage	ISCED
4	Early childhood education	Preschool	Preschool	0
5	Primary education	Primary school	First school	1
6
7
8				2
9
10			Middle school
11
12	Secondary education	Secondary school
13
14			Upper school
15				3
16
17				4