A former Ofsted chief, Lord Sutherland, is to head the inquiry into the embarrassing failure to deliver this year's Sats tests results on time.
Reports into what caused the delay will be presented in the autumn to the secretary of state for schools and to the exams watchdog.
A million children in England are still awaiting the results of tests taken by 11 and 14-year-olds.
Markers had been warning for months that the deadline could be missed.
There have also been persistent concerns from teachers about the quality of this year's marking - but Jim Knight said that the Ofqual exams watchdog had given assurances that "marking is at least as good as in previous years".
'Fair and thorough'
John Bangs of the National Union of Teachers has warned of "enormous" numbers of errors in the system this year.
Since May, markers had forecast delays amid warnings of administrative chaos in the processing of the tests taken by 11 and 14 year olds.
But ETS, the company awarded the £156m five-year contract to mark the tests, and the National Assessment Agency had offered assurances that problems would be resolved.
Last week, it was announced that the deadline would be missed - and pupils, parents and teachers are still waiting to receive the results - with many schools soon approaching the end of term.
Kathleen Tattersall, chair of Ofqual, has appointed Lord Sutherland to lead the investigation into what went wrong and she promises a "fair, thorough and transparent inquiry".
Lord Sutherland - formerly Stewart Sutherland - is a former chief inspector of schools and is currently provost at Gresham College in the City of London and president of the Royal Society of Edinburgh.
"I will report rigorously on the failure to deliver the results this year and make recommendations to ensure that this situation does not happen again," says Lord Sutherland.
There will be separate reports from Lord Sutherland - to Ofqual on the failure to deliver results on time and to Schools Secretary Ed Balls on the role of the National Assessment Agency and the Qualifications and Curriculum Authority.
In a letter to the chairman of the Commons schools select committee, England's Schools Secretary Ed Balls said the delay was unsatisfactory and "clearly unacceptable".
'All tests affected'
Markers of the tests, usually teachers, who contacted the BBC News website, had warned repeatedly that administrative problems and difficulties in contacting ETS meant that a delay was increasingly likely.
The volume of complaints rose in May, when the training process began, and again when many test papers were delivered to markers' homes late or not at all.
Questions were asked in the House of Commons, with warnings that the tests were turning into a "shambles". But the qualifications authorities said steps had been taken "to get things back on track".
The problems afflict all three test subjects - English, maths and science - but are said to be worst in English.
The online publication of the results of tests taken by 11 year olds has been delayed until 15 July.
Marking of results for 14 year olds will not be complete by then, but available results would be released by the end of that week so as many schools as possible had them before the end of term.