The Association of Educational Psychologists (AEP) said the introduction of a new three-year training course, in place of the current 12 months, for graduates attempting to enter the profession will lead to huge vacancies in the short term.
A scheme for the changeover was approved last week by a working group backed by the British Psychological Society.
From September 2006 training will switch from a one-year MSc course to a three-year PhD. But critics fear it will lead to no new educational psychologists being trained in 2007 and 2008. It is likely to exacerbate shortages already facing the profession.
Brian Harrison-Jennings, general secretary of the AEP, which represents 95 per cent of educational psychologists, said: "Educational psychologists can't work any harder than they already do. When there are two fallow years when nobody graduates, there will be even less access for schools to an educational psychologist than currently.
"They will probably only be able to get involved when a child has been excluded and the school is saying it can no longer cope, rather than doing preventive work. That is counter-productive for everyone involved, the child, the parents, the teachers and the school itself. It's a lose-lose situation.
"What is also very sad is the amount of bad outcomes for children who are not that extreme."
According to government figures, 113 out of 2,160 full-time posts in England and Wales were vacant last year, and 100 this year.
Terry Redmayne, director of the children, families and learning department in Middlesbrough, said: "Authorities that are recruiting will have to recruit from other councils. The impact of that will be very difficult to manage."