In a speech to the conference previewed in last Saturday's Independent, Mr Walker said: "A group of 40 sensible, well-behaved children, who know what to do and are willing to do it, is quite manageable."
Outraged members of the no-strike union rang its headquarters and several threatened to cancel their membership.
Mr Walker, 57, a retired special school headteacher and now a school inspector, said yesterday that he had "inadvertently expressed views which are quite outside PAT policy. I realise that the job of any national chairman is to uphold the policies of the association and to express the views of members - your views.
"In the circumstances, I have no alternative but to resign."
John Andrews, the union's general secretary, said Mr Walker, who has been a member of the association since 1971, had acted honourably and courageously. In his resignation statement, Mr Walker said that in a series of interviews on Tuesday, broadcasters had pushed him beyond his previous remarks.
t The conference passed a resolution warning that spoken communication could become extinct because children spend so much time using computers they have no time to converse.Reuse content