Hot school lunches are better for children than many maths and English lessons, Nick Clegg insisted as he defended the launch of a £1 billion free meals scheme.
Almost two million infants will be fed at their primary school at no cost to their parents from today under the Liberal Democrat policy, saving families up to £400 per year.
But critics have argued the money should be used in the classroom instead and council leaders have claimed that local authorities and schools are being forced to raid existing budgets to ensure that the plans goes ahead.
Mr Clegg has insisted that providing lunch for every five to seven-year-old at England's 16,500 primary schools will be more beneficial than some attempts to boost academic achievements.
He told BBC Radio 4's Today programme: "The evidence, and this has been exhaustively analysed, piloted, examined, is that giving a healthy hot meal at lunchtime is as, if not more, effective than many of the, say, literacy and numeracy initiatives which have been undertaken in the past in the classroom.
"It has a dramatic effect."
As the programme was launched, Mr Clegg vowed not to let critics "cloud" his goal of creating a level playing field for all children, adding that the scheme is "one of the most progressive changes to our school system for a long time".
Earlier this year, the policy sparked a coalition row over the expense of the reform, with former e ducation secretary Michael Gove and schools minister David Laws later writing a joint article insisting they were both behind the scheme.
Some headteachers also initially warned that the policy will cause difficulties in schools which do not currently have kitchen and dining facilities to feed all of their eligible pupils during the lunch hour.
A new poll published by the Local Government Association (LGA) earlier this month suggested that just weeks before the initiative is due to be introduced, some local authorities are facing a shortfall in the funding they need to ensure it can be delivered.
Government funding worth £150 million, in addition to the £1 billion to cover the cost of the scheme, was handed to councils to cover the cost of bringing school kitchens and dining facilities up to scratch.
The LGA's survey of 75 councils found that nearly half (47%) said they had not received enough money from the Department for Education (DfE) to cover the full cost of the work they needed to do to ensure that schools in their area were ready to provide universal free meals for infants.
The shortfall across those councils that responded totalled around £25.9 million, the association estimated.
Mr Laws said: "The evidence is clear. Providing children with nutritious and delicious meals gives them the fuel they need to excel both inside and outside the classroom, while making them more likely to opt for fruit and vegetables at lunchtime rather than junk food such as crisps.
"Schools across the country have done a truly fantastic job in preparing for this important milestone, supported by over £1 billion of Government funding over the next two years. Together, we will make sure that this landmark achievement delivers for pupils' health, their attainment, and for their hard-working families."
In a speech in July, Mr Laws insisted that there were very few schools that are not ready for the move.
Matthew Reed, chief executive of the Children's Society, said: "The extension of free school meals to all infants in the country is a positive step in the fight against child poverty. Our analysis shows that about 160,000 more children in poverty will be getting this vital support as a result of this historic move. It shows that the Government recognises the hardship that thousands of families are facing."
But he added: "For thousands of poor children in junior and secondary schools, nothing has changed. That's why it is vital that ministers build on this significant opportunity to make sure that every child in poverty is guaranteed a free school meal, whatever their age."