Professor Tim Brighouse, joint vice-chair of the Government's standards task force, wants ministers to include weaker students in the targets for 11-year-olds, which currently only cater for those children reaching "level 4" in the national curriculum tests.
His concerns match those voiced by the National Association of Head Teachers which this week said that schools should be free to set their own targets.
The Government wants four out of five 11-year-olds to be at level 4 in English and three out of four in maths by 2002.
But some educationists believe that this focuses on middle-ranking pupils, rather than those children with the furthest to go.
The GCSE league tables have faced repeated criticism for concentrating on pupils capable of getting grades A*-C in five subjects - at the expense of weaker pupils.
"We need more ways of motivating people to improve," said Professor Brighouse. "Otherwise there's a danger some pupils will will be left further behind and we are increasing the danger of social exclusion. Unless we get onto something that's more than those achieving level 4 and above, we will replicate the kind of focus on the CD grade borderline we have seen at secondary, "Just as we have moved to a points score for GCSE, so we should be moving towards the same thing at 11 - so that every child's performance matters."
Professor Brighouse, chief education officer in Birmingham, is encouraging his own schools to move in this direction. They are already working to increase the number of children reaching level 3.
He remains confident that the Government will move towards a points score for primary pupils: "I'm sure they'll embrace the notion that every child's performance matters."
The current target, he added, had been a good basis for progress.
NAHT conference, page 6