Restoring the cartons for primary pupils is one idea for a headline-grabbing initiative to be included in Labour's next manifesto.
Another option is to provide breakfasts.
School milk was scrapped for children older than seven by Baroness Thatcher in 1971 when she was education secretary. But growing concerns over children's nutrition could secure its return.
The move would be welcomed by Labour's grass-root members and would have symbolic appeal for party critics who believe Tony Blair is unwilling to dismantle Baroness Thatcher's legacy.
Stephen Twigg, schools minister, told the House of Commons that the reintroduction of free milk for all primary school pupils would cost pound;65 million a year.
He said that start-up costs would be about pound;21m to bring back the daily one-third of a pint for children in key stages 1 and 2.
Diane Cannon, project manager for the schools milk project at the Milk Development Council, said the Department for Education and Skills had asked them for a cost estimate.
She said: "Lots of children don't go to school with a proper breakfast or eat properly during the school day. Mid-morning milk breaks helps them concentrate."
Pupils under five who spend more than two hours a day in education still qualify for free milk in England and Scotland, while in Wales the age threshold has been raised to seven.
A DfES spokeswoman said it had no plans to reintroduce free milk for all primary children.