Children would go to school from 9am until 6pm, instead of the current hours of 8.30am to 3.10pm, and holidays would be slashed from 13 weeks to seven.
The radical plans are being drawn up by David Cameron's former policy chief Paul Kirby. He believes the measure would solve a wide range of issues, 'transforming the lives of most households in the UK within two years'.
He believes the extended days could reduce youth crime, boost education standards and prepare children for the world of work by getting them used to full days.
And it would also allow parents to return to full-time work, he says.
Conservative ministers are examining the plans, which would apply to all children between the ages of five and 18, in time for the party's 2015 general election manifesto.
Paul Kirby, a former close adviser to David Cameron, made his radical proposal for nine-hour school days on his blog this week.
Mr Kirby, a partner at accountants KPMG, believes that whichever party adopts his plan as the main plank of their manifesto could win the next General Election.
Mr Kirby said: "This is designed to allow all parents to work full-time without the need for additional childcare. "The average employment leave would cover all school holidays.
"The average working day would give most parents the chance to do a full time job, in between dropping off and picking up their kids."
Mr Kirby, who left Number 10 last year after being seconded from KPMG, says studies in America show that longer school days can improve children's education.
He claims that his plan would allow more women in Britain to enter the workforce and would give kids the equivalent of an extra seven years of education between the ages of five and 16.
Mr Kirby added: "This is about creating a lot of space in the day for play, creativity, relaxation and exercise.
"It's about making sure that kids don't fall behind or fail to understand.
"It's about schools opening their doors to let the wider community come in to help nurture and educate local kids."
But a National Association of Head Teachers spokesman said: "Most schools provide extended services for children and the nature of those services are best determined by those children's needs."
A Department for Education spokesman said: "We are already giving all schools the freedom to set the length of the school day and term.
"Many Academies and Free Schools offer extended opening hours, and we want more schools to take up these freedoms.
"We will obviously consider recommendations for further reforms."
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