Early Childhood Education, Primary Education, Secondary Education and Higher Education sections of the resource are all defined according to UNESCO ISCED 2011 classification. When writing your article please refer to the ISCED manual and ensure that in your article you cover the correct stages of education. 

Both the ISCED manual and ISCED mappings for a number of countries are available here: http://uis.unesco.org/en/isced-mappings

Articles in Childhood and Youth sections are defined according age:

Childhood: from birth to the age of 12

Youth: from the age of 13 to the age of 21