But she said that the government was determined to raise standards further.

Figures for all Scotland's schools, just published, show that 90% of pupils got five or more Standard Grades and 20% passed at least three Highers.

But there are wide variations between local councils. At one extreme is East Renfrewshire, where one child in three got at least three Highers - almost three times the success rate of Glasgow.

Mrs Liddell said the results give "important information for parents and the public on a major aspect of school performance".

Tribute

"Once again attainment at Standard Grade has risen," she said, "and though there has not been the same rise in Higher Grade, performance there remains consistent.

"I would like to pay tribute to the professional commitment throughout the system that has made this possible. We must all act together to push standards even higher over the next few years."

The Senior Chief Inspector of schools in Scotland, Doug Osler, said: "Parents should bear in mind that other factors such as the quality of learning and teaching, an ethos of achievement and the quality of leadership should be taken into account in judging the quality of education in any school."

'Value added' data

Individual schools will be giving parents so-called value added figures, showing how much they have improved pupils' performance between Standard Grades and Highers. But these will not be made publicly available nationally.

All such statistics fail to take into account the social context in which schools work.

In an attempt to address this problem the government is shifting its emphasis to setting school targets.

All secondary schools will have three-year targets. But critics say the measure of social deprivation they use - free school meals - is too crude.

Councils are due to publish the first set of targets - and how close schools are to hitting them - next month.