Many pupils were entered for qualifications that were too difficult for them and received low marks because of elementary mistakes, an analysis of the first year of National 5 reveals.
Teachers receive praise for they way they prepared students amid huge pressure, but unions have warned that if lessons are not learned from last year's fraught experience, the success of National 5 cannot yet be assured.
The reports, compiled by external assessors for the Scottish Qualifications Authority (SQA), identify the main issues picked up by markers. The first batch of reports, published today, covers the 10 most popular subjects.
Teaching unions complained vociferously in 2013-14 about the lack of support from the SQA in introducing the Nationals, highlighting the "unprecedented" workload that members had to bear. The external assessors' reports confirm that the first year of the qualifications went more smoothly than many had predicted. But unfamiliar elements caused problems, as did tasks that called for lengthy written answers.
Larry Flanagan, general secretary of the EIS teaching union, said that the challenges still facing schools should not be dismissed.
The reports show, for example, that a "significant minority" of students performed poorly in the geography coursework assignment - a new element - owing to "vaguely stated aims, little evidence of genuine research or overly descriptive responses".
Some students did no more than describe their main findings, "making little attempt to explain or evaluate them", and a number lost marks for directly copying from information sheets. Overall performance in geography, however, is described as "pleasing".
A number of maths candidates were "perhaps inappropriately presented at this level" and got very low marks. In one paper, the number of students unable to complete straightforward calculations was "disappointing" and schools are advised to offer pupils more opportunities to practise for the non-calculator paper.
Many history students attempted overly ambitious questions in their assignment or made the "quite damaging" mistake of not including a conclusion. But the assessors judge that most were entered at the right level, and they deem the exam to have been "demanding but reasonably fair".
Markers commented on the "unpreparedness" of some students for the physics assignment, in which they offered "little or no research". A large number of biology students lost marks in extended answers and chemistry candidates generally found essay-style reports difficult. However, the assessors conclude that schools did adequately prepare chemistry students for the different types of question that National 5 presents.
There is also good news for French teachers, who are told to be "very encouraged" by the first year of National 5 - even though some pupils were "clearly not presented at the appropriate level". Students are found to have coped "very well" with the English National 5, too.
But the most upbeat report is on modern studies, where the quality of teaching receives high praise and little evidence has been found of pupils having been wrongly put forward.
However, Mr Flanagan said there were still serious issues to overcome. "There may be some in senior management and policy positions within Scottish education who think that all's well that ends well as the National 5 results were sound," he said. "This is flawed thinking, which fails to recognise that the delivery of the Nationals was successful largely because teachers went the extra mile and endured substantial additional workload to ensure that pupils were not disadvantaged.
"If serious lessons are not learned, the risks to the smooth introduction of new qualifications remain significant."
Mike Corbett, a national executive member of the NASUWT Scotland teaching union, said: "There were concerns about new elements to courses which were often not explained or exemplified particularly well by the SQA, and there were worries over the standards to apply at National 5 - a situation which was not helped by the lack of consistent support from the SQA in some areas."
Teachers' "enormous efforts" had helped to mitigate the impact on pupils, he said, and he was encouraged that many of the problems were being addressed by the SQA.
Eileen Prior, executive director of the Scottish Parent Teacher Council, said the introduction of the Nationals "took Scottish schools down a miserable cul-de-sac of over-assessment, excessive workloads and finger-pointing between groups in the education establishment".
"The ones who suffered most in all of this were the young people who faced unnecessary assessment and high stress levels," she added.