About 11,000 GCSE students have been affected by an error by an exam board.
The humanities exam was taken in 150 centres
It forgot to send their schools the booklets of source material candidates needed to have in front of them to answer their humanities questions.
The exam on Monday was, for many, the first of this year's GCSEs and some were left "distressed" by the error.
The English exam board, AQA, told them to answer the questions anyway and said examiners would take its administrative error into account.
The source booklets were issued to the students in January. They include diagrams, tables of figures and charts to which they are supposed to refer in their answers.
They are not allowed to take those originals into the exam because they could have written notes on them.
But when their schools opened the exam papers they found the fresh copies of the source booklets were missing.
One school in Hertfordshire which contacted the BBC said its pupils were "distressed" by the error - particularly as this was their first formal examination.
One teacher, who wanted to remain anonymous, told the Press Association the questions would be "absolutely impossible" without the sources.
About 11,000 pupils in more than 150 schools and colleges in England were taking the exam.
One reassurance had been that at least they were all in the same boat.
But BBC News has learnt of one school in Suffolk which photocopied the source booklet and handed it out to students.
Student Joel Goodman said this also happened at his school in north London.
"A couple of minutes after starting the exam the invigilator came round and took the booklets away ... before making an announcement that due to an error, we weren't allowed to use them and that any questions that required the use of these sources could be left unanswered or with a mark saying 'no source booklet' or that we would have to put in maximum effort.
"A few minutes later, we were given the source booklets back again and allowed to use them. Due to the problem, we were given six additional minutes for the exam, as authorised by the co-ordinator of exams in our school."
Joel said he had been "somewhat confused" about what precisely was going on.
Opinions differ on the impact.
Emma Taylor in Keighley said: "I just nearly cried. I thought I could have done well on this exam.
"Humanities is one of my strong points and I just don't see how you can answer questions based on the sources you don't have. It just seemed stupid really."
Luke Fattorusso in Bedford said: "I took part in this exam and it was my first one under such conditions. I was totally put off by this error and believe we should be given the option to repeat the examination."
But Robert Locke in Aylesbury, Buckinghamshire, said that "contrary to what many people are saying", it was possible to complete the paper.
"It just required you to know the subject and to have studied the sources booklet supplied in January fully; much as with the old O-levels it is possible to complete the exam without the additional text, as the text is mainly there to jog your memory," he said.
"There were not questions directly refering to the sources booklet (e.g. what percentage on graph X) in the exam, just questions refering to the ideas within it".
The government's exam watchdog in England, the Qualifications and Curriculum Authority, said it was a "very serious issue".
A spokesman said: "We have asked to see copies of the paper immediately and for a full report from AQA.
"We do not underestimate the disruption and concern that this error has caused to candidates and will ensure that AQA acts so that every candidate gets valid results.
"QCA has also sought assurances that AQA has systems in place to ensure that this kind of error does not happen again."
Reports also came from teachers that AQA had been notifying schools of errors in an anthology of poetry and prose to be used in its English A syllabus exam on Tuesday morning.
These are said to include missing pages - more than 50 in some cases - as well as typographical errors or chunks printed upside down and back-to-front.
One of the main complaints is the short time schools have been given to check their copies and produce replacements if necessary.
AQA said it had been alerted to the problem last week. It believed it was confined to a small part of the print run.