Teachers have been reassured, repeatedly, that they would get national test papers marked and returned to them by Tuesday.
Since markers first began complaining about problems with the marking in February, the National Assessment Agency, England's exams regulator, has insisted the July 8 deadline would be met.
But, as The TES went to press this week, the NAA admitted that it could no longer confirm this, adding that it might need to extend the deadline for schools to appeal over papers, currently set at July 18, if they arrived late.
Any late return of scripts and results presents potential difficulties for schools, which are supposed to report test results to parents by the end of term.
Emergency marking centres have been running over the past six weeks in a bid to give every pupil a result by July 8. They were supposed to have finished by July 1, but The TES understands they will continue until at least Sunday.
ETS, a US assessment company, has encountered a host of problems since it took over marking England's national tests this year.
Examiners said they had received phone calls - some from ETS staff in the US - urging them to come to work at the emergency centres.
The news comes after 95 national test markers responded to an appeal by The TES for information on their work this year.
Only five said their experience had been broadly positive. The rest had experienced problems, with many using the word "shambles" to describe how the marking was organised. At least four had already complained to their local MP.
A primary school head, who is also a marker, said: "I shall check my school results thoroughly when they are returned. Were I to run my school in this way, I am sure Ofsted would put me in special measures."
ETS Europe has also faced huge criticism, with more than 8,500 comments from teachers and markers on the TES website. Much of the criticism has centred around erratic script delivery and computer system difficulties, as examiners have had to input pupils' marks on screen for the first time.
One teacher wrote that she had cancelled supply work in the expectation of earning pound;1,300 from marking test papers. But, even though she completed the training, the scripts never arrived. She stands to gain only pound;250 compensation.
Many markers have had trouble amending details on screen. For example, when schools have marked a pupil present on the online register but there is no script, the marker has to change this through ETS.
Many examiners have complained of difficulties getting through to ETS's helpline, and of emails going unanswered.
A key stage 3 marker said she had had to input 33,000 marks individually at the computer. A KS3 science examiner said he had got his girlfriend's 10-year-old son to do the data entry.
One marker sent a 13-page email to ETS detailing the trouble she had had registering 148 pupils' KS3 science results on screen.
The marker also said that a second school's scripts, which she was listed as due to mark, had not been delivered. This week, she said she still had the first school's papers.
The problems appear to have been widespread.
A very senior marker for a KS2 subject said that, as of last week, several of her team of nine supervisors had said some of the examiners for whom they were responsible had received no scripts to mark.
An email from one of the three most senior KS2 maths markers, dated June 19 and seen by The TES, says that in late May the senior team had been asked to provide a list of markers requiring scripts.
"Since then, it has been like roulette," the email said. "Some markers have received scripts; others still have nothing."
An email sent to a marker from a National Assessment Agency official suggests the NAA is not happy.
The email reads: "I am aware of issues concerning the service provided by ETS. Along with senior colleagues here at the NAA we have addressed these rigorously with ETS to ensure they take the necessary action. One of the problems has been the lack of response to queries."
An ETS spokesman said: "We believe that a great deal has been accomplished in a very short period of time. We made system improvements and quality improvements that will benefit schools, teachers and students in the long run."
Letters, page 26.