The Government has asked for contracts to be drawn up for key stage 2 tests in 2012, despite the promise of a review to determine the future of the exams.
In a letter to the Qualifications and Curriculum Development Agency, Education Secretary Michael Gove has set out a revised remit for the body until March 2011.
Work includes "secure timely preparation and procurement of National Curriculum test contracts for 2012 delivery".
The letter noted that a decision on the science sample testing in 2012 was still under consideration and a decision was due by the end of September.
The NAHT this week agreed to call off a potential boycott of the key stage 2 Sats next year following the government's promised review of assessment.
But Russell Hobby, the union's general secretary, told The TES he had not known that work was continuing on a new test contract.
He said: "I didn't know about this, but I don't know what it affects in terms of the review because it doesn't seem to me to pin down anything in 2012.
If it is exposing a pre-commitment that 2012 will be like 2011 that would be a problem, but I do not expect that to be the case."
The national curriculum review, which will be independently led and have input from a panel of headteachers, is due to report by spring 2011.
In 2008, American firm ETS took over the five-year tests contract, but the move ended in failure, with many test papers delivered late and the contract terminated early.
The QCDA was given nine weeks to carry out a procurement process, rather than the usual nine to 12 months, and awarded the contract to exam board Edexcel.
The Government announced in May that the QCDA will be closed, although some functions will be transferred to the Department for Education, Ofqual or the Department for Business, Innovation and Skills.