In a press release, UNICEF claims it provides "the first big picture comparison of the performance of schools in the world's rich industrialized nations."
UNICEF tried to provide a reliable overview of how each country's education system is performing and how it tackles inequality between poor and rich children.
Belgium takes 24th place and is bottom-of-the-table. Children from a poor social environment who go to schools with other poor children, only have a slim chance left to climb on the ladder.
"Countries at the top of this league such as Finland, Spain, Portugal and Canada are doing relatively well in containing inequality by not allowing their low achievers to fall as far behind as they do in other countries", UNICEF concludes.
On the other hand, countries at the bottom such as Belgium, New Zealand, Germany and the United States are allowing very wide gaps to open up.
Classmate can be five years behind
And there is more. "Overall, the report concludes that nowhere is there room for complacency. Large disparities in the achievement of pupils exist in every rich nation", the report continues.
"Indeed the gaps between the test scores of different children in the same school year can be so huge that some children are the equivalent of many school years behind most of their classmates."
"Even in the best performing country - Finland - low achieving 8th-grade pupils are approximately 3.5 years behind the average Finnish 8th grader in maths. In Belgium, Germany and New Zealand the low achievers are approximately five whole years behind.
"Non-native children particularly disadvantaged"
Non-native children are found to be particularly disadvantaged. In some countries, poor performance is more than three times higher among children of immigrant families than among other children.
This is the case in Austria, Belgium, Denmark, Finland and Germany, UNICEF says. Australia and Canada have a much better record.