Ken Livingstone was accused today of making an "unaffordable" pledge to reinstate the scrapped education maintenance allowance.
The Labour candidate has vowed to create a "London EMA" of up to £30 a week if elected on May 3. But an education expert cast doubt on his ability to find the £81 million needed to fund it.
Mr Livingstone wants to restore the EMA, scrapped by the Coalition, to en-courage teenagers from poorer households to stay in education.
Sixth-form or further education students would get the payment if their household income were below £31,000 a year.
Mr Livingstone said: "I have been struck by the plight of thousands of students who have had the lifeline that EMA offered snatched away while the part-time Tory Mayor stood by."
His London EMA would redirect existing funds in colleges and universities. He will ask councils to contribute and has conceded that he may have to use some City Hall money.
The Tory leader of Wandsworth council, Ravi Govindia, said: "This is an unaffordable cheque that he seems to have written on our behalf."
Professor Alan Smithers, director of the Centre for Education and Employment Research at Buckingham University, said: "It seems a fine idea but council budgets are very squeezed so it's difficult to see that many would make this a priority. At the moment it looks to be just kite-flying."
