The technique, called "dynamic assessment", tests the aptitude of people for particular tasks while avoiding the damaging stigma of pass or failure.
Candidates complete a number of work-related exercises, such as deciphering messages on labelling or identifying faults.
Although it has been used for about 15 years to gauge the capabilities of children with special needs or brain damage, dynamic assessment had not been applied to the field of employment until now.
Robert McHenry, chairman of Oxford Psychologists Press, the publishing company that markets the tests, said that traditional academic assessment effectively excluded those who had done badly. The Aptitude for Business Learning Exercises (ABLE), on the other hand, measured people's potential.
The New Deal trainees, most of whom had two or three poorly graded GCSEs, had shown much more interest and ability in the ABLE tests - figurative puzzles that stress problem-solving skills.
Mr McHenry said that under the test-and-prompt format of the assessment, some candidates had achieved full marks with just a few minutes coaching. "The outcome, particularly from people who had been disadvantaged in some way, was quite surprising."