OECD's best, Portugal could spend 38% less to produce the same number of secondary-school and university graduates as at present.

ECONOMIST: Can Portugal catch up with the rest of Europe?

The tests are the same for both primary and secondary school teacher trainees, who must also have achieved a grade C or above in GCSE maths and English.

BBC: Literacy and numeracy tests toughened for new teachers

In Colombia, for example, while most young people from rich households make it to lower secondary school, only around half from poor households get the same chance.

UNESCO: One in twelve young people in Latin America and the Caribbean fail to complete primary school and lack skills for work | United Nations Educational, Scientific and Cultural Organization

The timing of the row was suspicious: Mr Balls made the allegations at the same time as his department published figures showing that a fifth of youngsters transferring to secondary school had missed out on their first choice.

ECONOMIST: School admissions