There are now more than 100 empty posts in England and Wales, representing some 6 per cent of the current total, according to a new survey.
The British Psychological Society's division of educational and child psychology said at its annual conference this week that the shortage could become more acute, as the profession only recruits enough each year to match the number who leave.
At the same time local authorities are creating new posts to support schools faced with implementing the code of practice (Government guidelines which were introduced last autumn to regulate the help given to vulnerable pupils).
Steve Colwill, president of the Association of Educational Psychologists, which is affiliated to the National Union of Teachers and carried out the survey, described the shortage as extremely worrying. He said it threatened to undermine the good intentions of the code of practice by destroying long-term, preventive work in schools. "It will mean that authorities will find it very difficult to keep to the time limits introduced by the code of practice, " he said.
The concern is shared by the BPS.
"The funding for the training of educational psychologists is wholly insufficient," said Ingrid Lunt, chair of the society's professional affairs board. "There's a blockage in the system because the funding is virtually impossible to obtain.
"There's an urgent need for a Government review of the training, recruitment and employment of educational psychologists. Local education authorities may even find themselves unable to carry out their statutory responsibilities.
"Then there is the problem that EPs are becoming less able to do preventive and consultative work with schools, particularly before the stages of statutory assessment.
"EPs have a crucial contribution to make at stages one to three of the code of practice - early identification, in-service training and working with parents and teachers. The shortage is forcing them to limit their work to stages four and five - the drafting of statements."
The code of practice was set up under the 1993 Education Act and lays out the duties of schools and local education authorities.
It addresses long-standing criticisms of LEA behaviour by setting new time limits for the completion of statements (the formal promises of help for individual children), and new standards for their clarity.
The major departure, however, is the code's insistence that schools should carry a predetermined share of the burden. They must use their own money to try to solve problems before they can ask for additional help from the LEA.
The teaching unions believe that this will require training for their members, particularly in primary schools, and more help from educational psychologists.
The Government, however, insists that the code will involve no additional costs.
Educational psychologists are in a difficult position because they want to see not only more trainees, but also more training. Practitioners at the conference favoured abolishing the time-consuming requirement that they must first qualify as teachers.
EPs say they feel increasingly cut off from their clinical colleagues and see a more rigorous training as a move towards staying in touch.
They say the problem is made worse because authorities will not pay for training unless they have an immediate need of their own.