The data focuses on compulsory years of schooling, which is typically from around age 6-16 in most countries. The pre-school, lower secondary and upper secondary levels are also very important for students with disabilities, difficulties and disadvantages (DDD), but generally there are fewer data available.
The data are presented for each category of disability, difficulty and disadvantage and are broken down according to place of education for students receiving additional resources (special schools, special classes, regular classes, and total number of students for all settings in that category).
The number of categories used varies widely from country to country, as do their national labels. The data also show the classification of students in receipt of additional resources in the three broad cross-national categories of disabilities, difficulties and disadvantages. Those in the "disabilities" category (A) have clear organic bases for their difficulties. Those in the "difficulties" category (B) have learning and behaviour difficulties which do not appear to be due to either a clear organic basis or social disadvantage. Those in the "disadvantages" category (C) receive additional educational resources due to aspects of their social and/or language background.