Thomas Hards, 10, cannot go to his preferred secondary school in September, even though there are vacancies, because he is too clever.
He has been placed by Lewisham in band 1 after sitting the London Reading Test and all the places for that group at Crown Woods School, Greenwich, are full.
But his mother Donna does not agree with the arguments about balance and fairness in comprehensive schools. She wants a decent education for her son.
"I'd be quite happy for Thomas to go in at a lower band but it's not allowed, " she said. "It's absolutely crazy. Lewisham and Greenwich want to put bright children into bad schools to make them better. But I'm not having my son used as a pawn. I know parents who have told their children to fail the London Reading Test so they can get a place at the school they want. I wish I'd done the same," she says.
Peter Wells, head at the 2,050-pupil school, dislikes banding. Each year there are up to 30 vacancies in the lowest-ability group, band 3, he says, even after first and second preferences have been catered for.
"The governors and I have made representations to Greenwich that when there are vacancies after first and second preferences have been filled places should go to pupils on the waiting list in other bands," he says. "But they are not prepared to move in that direction."
Lewisham parent Michelle Hyder's above-average son Paul, 11, cannot go to Addey and Stanhope, Lewisham, because it is full, yet nearby Sedgehill has refused a place. The family has been offered two schools which recently received bad OFSTED reports.
Mrs Hyder said: "It's just ridiculous. The Labour council says everybody has a choice but that's just not true. If we lived in Bromley, where there are grant-maintained schools, we could apply to as many as we liked."
Jane Smith, whose band 1 daughter Emma-Jane,10, has also failed to get into Addey and Stanhope, says: "You encourage children to do well and then they are penalised for it. Why should I send my bright child to a school no one else wants just to try and improve its reputation?