A renewed confidence in its own ability to handle large amounts of data has led the Scottish Qualifications Authority to reject any change this year to the way schools and colleges report the outcome of internally assessed units in Higher Still.
Critics, however, say the SQA has deliberately left it too late to make agreed changes and warn it could now be swamped by vastly increased numbers of unit results.
Meanwhile, SQA bosses were hauled in on Wednesday to explain their decision to ministers, who are said to be "disappointed".
Billy MacIntyre, interim director of awards, defended the controversial move. "Any changes we're making to the system this year have to be mission critical. If they're not mission critical, we will not change," Mr MacIntyre said.
The volte-face displays a growing assurance within the authority that its internal reforms are making a significant difference. Its surprise decision overturns a previous announcement last November by Jack McConnell, Education Minister, who backed a local authority proposal to simplify assessment reporting.
Mr McConnell said the SQA would treat all units as a pass unless schools and colleges informed it that candidates had failed, or had their results deferred or withdrawn.
This would have cut the volume of information travelling between centres and the SQA by two-thirds. But a two-month SQA review has ruled out what became known as the "default pass" agreement.
Mr MacIntyre said: "On balance, having assessed it from a risk perspective, we concluded those risks are too great and we will retain the system we used last year but obviusly with the necessary improvements to make sure it works effectively."
Schools, he said, believed errors could creep in with the revised proposal, allowing candidates to pass who were not entitled to.
Last year there were 1.5 million national unit entries with a pass rate of 72 per cent. "The risk is therefore 28 per cent. That's the bit of our result base that could be wrong," Mr MacIntyre said.
Returns from schools and colleges reveal a 40 per cent increase in the number of unit assessments this year because of new courses at Intermediate and Advanced Higher levels, a rise the authority is confident it can handle by restructuring its data-processing and certification unit. Registrations and candidates' entries are also being checked and rechecked with exam centres, it says.
Teachers will be invited to begin submitting unit results within a fortnight and will have until the end of May to conclude their assessments, leaving a full month for the authority to follow up missing data.
Ronnie Smith, the Educational Institute of Scotland's general secretary, said: "It's their call. They run the system but they won't get much quarter if things go wrong."
Michael O'Neill, education director in North Lanarkshire and joint originator of the "default pass" approach, this week wrote to his own headteachers expressing astonishment at the decision.
His co-originator, Judith Gillespie at the Scottish Parent Teacher Council, said: "I have moved from the camp that said this year's exams will be all right, to being very dodgy."
Gordon Mackenzie, president of the Headteachers' Association of Scotland, described the reversal as "disappointing".