By Gary Eason
BBC News website education editor
The way Highers exam results for Scotland's schools are published is potentially misleading, the official statistics watchdog has said.
Schools' results need to be clearer, the statistics watchdog says
In some schools the percentage who stay on beyond the age of 16 is given as more than 100%.
And the proportion of pupils gaining qualifications is said to be more than all those actually in the year group.
The Statistics Commission said such results would tend to "undermine public confidence in official figures".
Following enquiries by the BBC News website, the Scottish Executive Education Department (SEED) is to change its explanatory notes on this year's results.
The school-by-school figures are due to be published on Wednesday on the Scottish Schools Online website.
It is going to reconsider the way the results are presented for next year, taking into account what the Statistics Commission has said.
The problem does not affect the exam results of individual pupils.
It has to do with the way these are combined to show the performance of their schools.
It arises because the department tries to show the eventual success, in gaining qualifications, of all those who start the fourth year of secondary school (S4).
Most will turn 16 during the year and can leave school, but ministers are keen to raise Scotland's skills level so want to encourage them to stay on in education into a fifth or even sixth year and beyond.
So the proportion of fifth year (S5) pupils in each school achieving Higher awards is given, not as a percentage of those who took the exams, but as a percentage of those who originally began the fourth year.
The trouble is, that number can have fluctuated as pupils come and go.
And some schools take in extra pupils at S5 as a matter of policy - typically from schools which cater only for those up to S4.
So their "staying on" rate can be more than 100%. In other words, more are said to have "stayed" than were there in the first place.
It is not possible to tell from the published results how many of those who actually sat Highers achieved them - and the attainment "percentages" can also be more than 100.
This can happen in the Standard Grade exams children take at the end of S4, too, if anyone has joined the year group since the census was taken at the start of the school year the previous September.
Last year at the independent St Mary's Music School in Edinburgh 143% of those in the fifth year are said to have achieved at least one Higher.
But we have now obtained figures from SEED which show the attainment of pupils in S5.
At St Mary's, the figure was 100%.
In schools where the figure is affected but less than 100%, the problem is not so obvious.
At Edinburgh Academy, for example, the published attainment - based on the S4 roll - was 95%.
But of those actually in the fifth year it was 75%, according to the education department.
But even these results from SEED - based on the S5 roll - can be misleading.
The rector of the Edinburgh Academy, Rev John Light, said that in fact 92% of his pupils last year got at least one Higher.
"I agree wholeheartedly with your contention that the SEED figures are grossly misleading," he said.
"I believe that statistics such as these, which 'measure' publicly a school's performance without any prior check with the school about actual results or the broader picture, are pernicious.
"If one single school is damaged or weakened by misleading information, SEED has failed in its main function, which should be to support and promote good education in all schools in Scotland."
There is no suggestion that there is any attempt deliberately to deceive anyone.
But the Statistics Commission's chief executive, Richard Alldritt, said: "Some aspects of the presentation of results in Scottish Schools Online could be misleading to parents and others.
"Showing percentages that exceed 100% will also tend to undermine public confidence in official figures more generally and isn't necessary.
"There are other ways in which the figures can be presented to avoid this."
He has been in touch with the education department, seeking changes.
Mr Alldritt is sympathetic towards the underlying motive and says there is "no simple answer".
But he wants the department to "unpack" the main components - staying on between years four and five, and the proportion achieving a specified level in the examinations.
SEED's senior statistician, Pete Whitehouse, told the BBC News website the presentation of the statistics had evolved over time "through an ongoing process of engagement with users and providers".
One of the reasons for it was "to enable users to draw conclusions and to provide the basis for questions".
But he said he would be updating the guidance notes for this year's results.
"I will also be working with colleagues to explore whether we can improve the communication of results for the June 2006 examination diet.
"The views of users and providers, including the Statistics Commission will be brought into this discussion."
He said showing the actual attainment of fifth year pupils could be "open to the criticism that low attainers could be 'encouraged' to leave at S4".
The Scottish National Party's education spokesperson, Fiona Hyslop, said "the executive should not be letting down pupils by misrepresenting their achievements".
"Measuring percentage Higher achievements for S5 by the previous S4 intake may have been the accepted norm for tracking achievement, but this does not necessarily mean this method should continue to be used.
"We need a robust and open system of gauging pupils' results."