MSPs are seeking assurances from the Scottish Government that pupils will not be handicapped if their schools are unprepared for the exams brought in to replace Standard Grades.
Around 65,000 S4 pupils are studying for the new Nationals, with the first candidates due to sit the exams in April.
But there is growing concern that schools are so far behind they will not do test papers, or prelims, usually sat in November or December, until April - just a month before the final exam in some schools.
Opposition MSPs have called on education secretary Mike Russell to provide a "cast iron assurance" that examiners will take into account some schools are being better prepared than others.
Scottish Labour's education spokeswoman Kezia Dugdale said: "The new examination system will naturally raise concerns about how they will run before they are introduced.
"What these concerns reflect is that, once again, Mike Russell and the SNP simply plough ahead with their reforms regardless of the warnings they receive or the concerns they hear."
The Curriculum for Excellence (CfE) was introduced by the SNP four years ago and set out to place the emphasis in schools on choice, creativity and cross-subject learning.
Earlier this year the Educational Institute of Scotland (EIS), the country's largest teaching union, found two-thirds of those taking part believed they had "unsatisfactory" levels of support to implement Curriculum for Excellence (CfE) in the later years.
A Scottish Government spokeswoman said: "Schools have made excellent progress in delivering the new qualifications and we are fully confident that this year's diet will be delivered to the benefit of pupils across Scotland."
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