Children in deprived areas are being denied access to extra curricular activities because they are too expensive, a report has found.
Funding for clubs rarely covers their costs, meaning affluent families who can afford to pay are most likely to benefit from them.
The findings will worry the Government, which has prioritised activities outside the classroom as a way to tackle the achievement gap between rich and poor children.
It's Children's Plan, published this week, called for greater opportunities for all children, with special help for disadvantaged areas.
The report, by New Philanthropy Capital, After the bell, finds that schools and charities operating after-school clubs "often run on a shoestring or rely on the energy and goodwill of a few volunteers". It follows the revelation in The TES that extended school services in a number of deprived parts of the country are being forced to close because of lack of money.
Ministers have called for extended schools to be available from 8am to 6pm by 2010. But services at many schools will close this term as charity providers struggle to make ends meet.
As well as specific extended school activities, the NPC report includes other school-related clubs. A number are aimed at vulnerable children in poorer areas.
The greatest challenge to schools is finding ways to make the clubs sustainable, the report finds.
"Without a coherent long-term strategy for provision, the benefits are likely to remain small-scale and short-lived," it says. Government funding is not ring-fenced, which means the priority given varies between schools. Guidance to councils on extended schools is that services should be funded if they can be sustainable.
According to Schoolfriend etc, a charity running more than 1,000 after school clubs, this has led some councils to establish clubs only in richer areas, where parents can afford to contribute. The charity will shut down services to 150 schools this term.
Anne Longfield, chief executive of children's charity 4Children, said: "In theory, the money is there but it is so complicated that parents and providers cannot find their way through the system."
Applying for funding is too complicated, the system needed simplification, and people locally should be given more say, she said. The Department for Children, Schools and Families has committed pound;1.3 billion to fund extended schools over the next three years, which includes pound;265 million for children in disadvantaged families.
Research by the Joseph Roundtree Foundation found that out-of-school activities allowed young people to build more equal relationships with adults than those in the classroom.
One scheme recommended by New Philanthropy Capital, which advises charitable donors, is IntoUniversity, run for children in disadvantaged areas by the Sutton Trust.
Sir Peter Lampl, the trust's chairman, said: "Securing funding is a constant challenge for many organisations, and without it the most vulnerable children will be the ones to suffer first."