The Scottish Qualifications Authority (SQA) has provided schools with only a single specimen paper for each national qualification.
Pupils are having to rely on relevant sections of previous exams, such as Standard Grade, to give them more examples of the likely questions they will face.
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The issue was raised at a meeting of the Scottish Parliament's education committee, which is looking at the rollout of the Curriculum for Excellence (CfE) and its associated exams.
Larry Flanagan, general secretary of the Educational Institute of Scotland (EIS) teaching union, told the committee that schools should have at least three sample papers to revise from.
He said: "A key issue is that people need access to practice papers. There is obviously no history of past papers as this is a new qualification.
"In our view, schools need to have access to at least three practice papers for the new qualifications in each subject to allow pupils to prepare for sitting the exams. These materials are needed in schools now to allow pupils to develop their exam technique before May."
He was backed by SNP MSP Joan McAlpine, who expressed surprise over the situation and said teenagers needed to practise before sitting exams.
However, Dr Janet Brown, chief executive of the SQA, said there had been significant concerns in the past about pupils being asked to sit multiple preliminary exams and that the purpose of CfE was to reduce assessment.
She said: "One of the things we wanted to do was reduce the number of practice prelims that pupils were trying to go through.
"CfE includes a large element of coursework that counts towards the final qualifications, reducing the need for practice prelims.
In some cases we were hearing of students undertaking two or three preliminary examinations, which I think is a real challenge for students."
Dr Alasdair Allan, the minister for learning, added: "I am happy to talk to the unions about this, but what has been provided is adequate. We will continue to listen to feedback and to work with teachers, pupils and parents in delivering lasting improvements that will benefit our young people and economy."
The committee also heard concerns that the Scottish Government's decision to allow some schools to delay the introduction of new Higher courses for a year if they did not feel ready was being ignored by council directors of education.
Mr Flanagan said the EIS had written to nine local authorities expressing concern that they were enforcing a blanket approach to moving to the new Higher despite concerns about a number of subjects including computer science, physics, biology, chemistry and maths.
However, Mr Allan said he was not aware of any such blanket approach, and officials from Education Scotland said they would be advising against such an approach.
Earlier, the committee heard the Scottish Secondary Teachers Association (SSTA) raise concerns about the amount of work linked to the new curriculum, with some teachers saying they have to work more than 60 hours a week.
However, the union acknowledged some schools were making additional unnecessary work for themselves through a misunderstanding of the assessment criteria and a desire to get it right.