Tony Blair has met head teachers of private schools to encourage them to sponsor city academies.
Mr Blair has set targets for the number of city academies
The government wants 200 of the flagship schools, which must raise £2m themselves before receiving extra state help, to be built or under way by 2010.
Private schools are eligible to sponsor academies, which ministers hope will improve standards in deprived inner-city areas in England.
Downing Street described the meeting as a "relationship-building exercise".
A spokeswoman added: "It is part of the whole programme of engaging people in the city academy programme.
"We make no secret of the fact that we do want to engage and encourage potential sponsors for city academies."
She said heads and governors of private schools had attended the Number 10 event but would not give details of the guest list.
The academies attract extra public money in return for private sponsorship.
Each must raise £2m towards the costs of opening and sponsors are then given influence over the direction of the schools and the appointment of governors.
The government pays the rest, which is typically around £25m.
The 18th such institution - the Lambeth Academy in south London - was opened by the Queen on Tuesday. Another 36 are in development.
The school standards minister, David Miliband, was also at the Downing Street reception.
In 2002 - when the first academies opened - he announced the plan to allow private schools to sponsor them, to "overcome a history of rivalry, resentment and suspicion" between the sectors.
"The Eton Academy, the Winchester Academy - it does have a certain ring to it," Mr Miliband added.
But private schools have not rushed to take up the idea.
Marlborough College in Wiltshire has expressed an interest in collaborating with a school in Swindon - but would not be putting in any money.