Publishing poor primary school figures on the same day as GCSE results could be interpreted as an attempt "to bury bad news", the Conservatives say.
The Department for Education said the results received widespread coverage
A number of e-mails obtained by the Press Association suggest that civil servants had warned against the move, but their objections were over-ruled.
Senior Tory David Willetts said releasing the results on the same day reduced public scrutiny.
But the Department for Education said it had followed the correct procedures.
The primary school test results were published at exactly the same time, 0930 on Thursday, 24 August, as GCSE figures.
In previous years the results were released on separate days.
The primary school figures showed falling standards in reading, writing and maths among seven-year-olds and missed targets for 11-year-olds.
According to e-mails sent on 12 July and obtained by the Press Association, some officials were concerned about when the statistics would be released.
Among them were Tracey Beames, from the Strategic Communications Planning Unit, and Ruma Multani, a press officer for the Department for Education and Skills (DfES).
Ms Multani said: "We can't publish the GCSE and KS1 and 2 (primary school) stats on the same day.
"Last year we did the KS results on the 23rd Aug and the GCSE results on the 25th.
"Can't we do them a couple of days before the GCSE results?
"Also, we usually hold a press briefing for the KS results in which case ministers will not want them on the same day."
Code of practice
But Andrew McCully, DfES director of standards, wrote back that the release of Key Stage 1 and 2 statistics had already been discussed at a high level.
"Ruma, this has already been discussed with John and with special advisers. We positively want it to be 24th. Andrew," he said.
Ms Beames later wrote: "On this basis - happy with 24th Aug for KS1/2 stats."
The e-mails came to light in a reply from the DfES to the Statistics Commission watchdog, which has asked why the timing of the primary school figures was changed this year.
According to the code of practice, government figures should be released as soon as they are available and at a time which promotes "widespread access and informed debate".
The commission is expected to accept that 24 August was the earliest date the primary school statistics could have been published.
For the Conservatives, Mr Willetts, the shadow education secretary, said: "Publishing all the results on the same day diminishes the scope for public scrutiny.
"The e-mail correspondence reveals that it was special advisors, acting on behalf of ministers and not statisticians, who determined the date of publication and pressed for a release of all three results on the same day.
"I believe it is wrong for political advisors to make decisions which reduce the public scrutiny of exam results.
"This has the whiff of previous scandals about 'burying bad news'."
Mr Willetts is writing to the Statistics Commission asking them to tell the DfES to publish the figures on separate days in future.
However, a spokesman for the DfES said: "Publication of the data was carried out in accordance with the rules governing the publication of national statistics.
"The department's chief statistician has confirmed to the Statistics Commission that the correct procedures were followed.
"In turn, the chief executive of the commission has advised us that he is content that August 24 was indeed the earliest date that these statistical results could be released."