ETS Europe Senior executives from Sats marking company ETS appeared before a specially convened meeting of the Commons select committee for children, schools and families last week to put their side of the story in this summer's shambles.
They accepted some of the blame, confessing to quite serious problems with their computer and tracking systems.
For example, they said there was a glitch in an online system on which schools registered whether or not pupils actually took the tests. This meant that the company did not know whether the pupil was absent or if their script was missing.
But the executives said that the National Assessment Agency (NAA) shared "significant responsibility" for the failures, having made five major changes to the contract ETS signed in the lead-up to the tests. This left the company struggling to cope with much more complex arrangements than expected.
Crucially, the executives said the NAA changed the arrangements it had agreed for the training of markers only two months before the tests were taken.
ETS also said the NAA did not make it aware of previous problems with Sats, including difficulty in recruiting markers.
The verdict: NAA dithering over arrangements for the training of examiners is likely to have contributed to the chaos, but this summer's problems went far deeper.
ETS was planning to conduct much of its marker training online, so the NAA's decision in March to veto this left the company desperately trying to organise face-to-face training at short notice. Markers were soon complaining about not finding out about training until the day before, or being sent to the wrong event.
What ETS failed to mention, however, was that it was the technical problems with its own online training pilot, conducted last November, that lay behind the NAA's decision to abandon it.
Also, the company's relationship with the NAA fails to account for numerous other problems this year, including software systems malfunctions, non-delivery of scripts to markers' homes, and examiners' frustrating experiences with the helpline.
Degree of responsibility: 8.510
QCANAA Ken Boston, chief executive of the Qualifications and Curriculum Authority (QCA), told the select committee in July that he "apologised for the failure of our contractor" to have results ready on time.
He appeared to blame ETS for inadequate marker recruitment and retention; examiners being given the wrong information about training; delays in getting papers to markers; and the helpline problems.
Mr Boston admitted that the QCA, of which the NAA is a part, was responsible for running the process that selected ETS. But he said others were involved too, including the Government itself, and the QCA could not be held responsible for every detail of ETS's performance.
The verdict: The QCA was right to argue that many of the problems lay with the detail of ETS's operation. No other contractor in the history of Sats has presided over chaos on the scale of this summer, and it is hard to avoid the impression that the US firm's inexperience of the English system was a factor.
That said, the QCA had nine months during the procurement process, before ETS was selected, to make sure any potential difficulties were ironed out and that the company was fit for the job.
The authority also approved a number of changes this year that made the operation potentially more tricky. These included altering script delivery arrangements, stopping markers being given scripts in advance of training, and changing the system for checking the quality of marking.
Degree of responsibility: 810
The Department for Children, Schools and Families argues that it is not responsible for the detail of the marking arrangements.
Jim Knight, schools minister, told the select committee in July that "matters to do with the contractor are for the QCA, and its agency, the NAA, to answer". He added, however, that he had read reports of markers' concerns in The TES and had raised them with QCA and NAA officials. Up until late June, they had reassured him that "things were on track".
The verdict: The Government did have some involvement in the decision to appoint ETS. It had a representative at meetings where the procurement was discussed, and the Office of Government Commerce, an arm of the Treasury, approved the process.
While it is fair to say that ministers were not involved in supervising the details of the marking arrangements, it is likely that at least some of this year's changes were known about by civil servants, who shadow their QCA counterparts very closely.
Some critics will feel frustration that no elected politician was prepared to take responsibility when things went wrong.
Degree of responsibility: 4.510.