Ministers say not enough schools have responded to requests for information for the staffing survey, last carried out in 1996.
But opposition parties and headteacher associations are suspicious of the delay. They believe a survey is needed every other year to help set recruitment targets for teacher training and decide which subjects get extra incentives, such as pound;4,000 "golden hellos".
David Miliband, school standards minister, said only 174 of 800 volunteer schools have responded. Government statisticians say they need data from more schools for the survey to be accurate.
The full results will be published, as scheduled, in September.
But David Hart, general secretary of the National Association of Head Teachers, said schools needed the information now, as they consider budgets and possible staff cuts.