In a major survey, they say that while overall standards have risen, schools with similar pupil intakes perform very differently.

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Although two out of five secondary schools are consistently good, one in 10 has significant weaknesses and just over one in 50 fails to provide an acceptable quality of education.

Responding to the report, the Schools Standards Minister, Stephen Byers, said the government was concerned about the proportion of schools with significant weaknesses and would shortly be publishing proposals to reduce their number.

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The findings, published by the Office for Standards in Education (Ofsted), are based on the inspections of every one of the 3,594 secondary schools in England between 1993 and 1997.

Inspectors examined the standards achieved by pupils, the quality of teaching, the effectiveness of school leadership and management, and a range of other indicators including pupil behaviour.

The Chief Inspector of Schools in England, Chris Woodhead, said the report was the most comprehensive analysis of secondary education ever published.

"The overall conclusion is that standards are certainly improving," he said.

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"The challenge now is to improve the performance of the one in 10 schools which has serious weaknesses and to narrow the unjustifiable gap in standards attained by schools serving similar communities."

Mr Byers said the report showed good progress was being made by secondary schools, but there were no grounds for complacency.

"One of the most worrying aspects of the report is the way in which schools with comparable intakes perform very differently.

"This government believes there must be no hiding place for under-achievement, which is why we will ensure that every secondary school has its own targets for achievement at 16."

Mr Byers said it was a matter of great concern that one in 10 secondary schools - more than 350 - were found to have have significant weaknesses.

"The government has shown clear resolve to tackle failing schools. We must now act on those schools with significant weaknesses. We shall shortly be publishing our proposals.

"Good quality education must not be left to chance. It should be a right not a lottery."

Market reforms

But head teachers' leaders blamed the performance gap on the market-driven reforms of the last decade.

The general secretary of the Secondary Heads Association, John Sutton, said: "League tables, naming and shaming of schools, coupled with enhanced parental choice, have inevitably meant that favoured schools have found it easier to produce improvements.

"Unless the government is able to attract the best young graduates into the profession and persuade them to work in the more disadvantaged schools, and provide those schools with adequate funding, the gap is set to widen even further."

Ofsted inspections which pilloried failing schools made it even more difficult for them to attract good heads who might turn them around, he said.

The general secretary of the National Association of Head Teachers, David Hart, said the Ofsted report gave schools overall a "fairly comprehensive clean bill of health".

"Obviously the number of schools showing serious weakness needs to be reduced, but no-one should under-estimate this task," he said.

"There are real difficulties encouraging heads to take over such schools."