Lack of time to implement this year's Sats tests creates increased risks of the system going wrong again, according to the man who led the official inquiry into last year's test fiasco.
Lord Sutherland said that key stage 2 tests would have to be rigorously checked to ensure there is no repeat of last year's delays.
The exam board Edexcel was appointed only this month to replace the disgraced American firm ETS, whose five-year contract was terminated.
"It's going to be done in a much more constrained time scale this year, and that puts pressure on the system and creates greater risks," Lord Sutherland told The TES.
"There is increased risk and there will have to be rigorous monitoring to make sure any problems are dealt with on the spot."
He criticised officials this week for failing to carry out proper checks on ETS Europe before giving them the contract. Concerns about the company could have been discovered by "googling" it, he told MPs.
Lord Sutherland, who took over this week as the new chairman of the Chartered Institute of Educational Assessors, said it was crucial that examiners were given better training to help avert further problems.
"There was a problem with advising the markers, who did a marvellous job in difficult circumstances," he said. "The lack of support needs to be rectified, so it does not happen in any kind of public examination."
Lord Sutherland said examiners and assessors should have more say in how the system is developed and called for expert marker panels to be established to advise officials.
He also wants to see greater training for teachers whose assessment skills will come under greater pressure with diplomas and the possible introduction of single-level tests.
The Chartered Institute of Educational Assessors wants to have 3,000 qualified chartered educational assessors working in schools in the next three years to support teachers.