Stung by accusations that his reforms have neglected secondary schools, President Bush has vowed to put America’s troubled high schools at the centre of education policy if he is re-elected.

He has called for compulsory high school “graduation” or exit exams for 18-year-olds and the introduction of annual standardised tests for all 13 to 17-year-olds.

As is the case with tests that are already compulsory for pupils aged eight to 13, the results will determine which schools will face sanctions under Bush’s reforms.

The criticism was fanned by the release last week of league tables ranking the US a poor tenth among industrialised nations in the proportion of 25 to 34-year-olds completing secondary school. The tables, published by the Organisation for Economic Co-operation and Development, also showed the US slumping from fifth spot among those aged 35 to 44.

Accusing the White House of failing to curb high dropout rates, Democratic presidential challenger John Kerry has vowed to increase numbers of pupils completing high school by one million. He is targeting secondary school reforms in the run-up to November’s US election.

A staggering 30 per cent of high school students drop out, including nearly one in two Hispanics and blacks, said Jay Greene, a researcher at the Manhattan Institute think-tank. Of those graduating, only half complete the coursework necessary to apply for regular degree courses, while one in three college entrants must take remedial classes to get up to speed.

The Bush administration’s No Child Left Behind schools legislation has focused on performance in primary and middle schools at the expense of high schools. Overhauling secondary education is “long overdue,” said Gerald Tirozzi, executive director of the National Association of Secondary School Principals, who branded it “the stepchild of school reform”.

Answering his critics, Bush has mapped out an agenda for the next four years that would include early intervention to keep wayward pupils in school and $200 million for teachers to use test data from 13-year-olds to tailor student learning plans.

But there are concerns that test pressure could drive out weaker pupils, Mr Tirozzi said. In recent scandals in New York and Texas, schools were accused of enouraging struggling students to leave rather than lower schools’ scores.

High school exit exams - so far taken or planned in 25 states - are rarely geared to higher education or jobs and often only measure skills aquired at 15 or 16, a recent report by the Center on Education Policy found. All exit exams cover English and maths, and some also cover science and social studies.

The most promising reforms centre on breaking up campuses into smaller learning communities, promoting personalised supervision that would make it harder for students to slip through the cracks. Extensive small-school initiatives already underway in Boston, Chicago and New York have been endorsed by both Mr Kerry and Mr Bush.

Mr Kerry has also proposed revoking dropouts’ driving licences to keep students in school.