Ministers announced in January that the pound;26 million key stage 3 ICT test, due to be introduced into league tables from 2008, was being made voluntary - although schools are still being advised to get their pupils to sit the test on an optional basis.
But Naace, formerly the National Association of Advisers for Computers in Education, said the move might lead schools to place less emphasis on the subject.
The decision on the test was recommended at a Qualifications and Curriculum Authority meeting. Minutes from the meeting state that unnamed board members argued ICT was best taught "embedded" in other subjects, rather than discretely.
Jim Merrett, a Naace spokesman, said: "Most people within Naace feel that it's not sufficient to just teach ICT skills within other subjects, because the subject teacher will not be focusing on ICT."
But some of the association's 2,400 members have welcomed the move. Having it as a statutory assessment would have meant too much time preparing for the test rather than promoting deeper subject understanding, they said.
They believe that allowing pupils to sit the assessment when their teacher thinks they are ready, as proposed, will make it more useful for checking their strengths and weaknesses.