There is one policy change that could fix some of Australia's biggest problems of rising inequality, slowing economic growth and slipping education rankings, according to two eminent international researchers.

It's preschool. Oxford University's Edward Melhuish and Rutger University's Steve Barnett are visiting Australia for a series of talks, calling on Australian governments to extend public preschool to 3 year olds as well as 4 year olds.

"They're definitely learning, it's not just a free-for-all playtime": Emilie Capes, with husband, Jeremy, and their children Thomas 5, Josephine 3, Charlotte 2. Credit:Kirk Gilmour

That's because the weight of international evidence shows that the achievement gap when 5 and 6 year olds start school carries all the way through (if they don't get targeted help) and impacts on social adjustment and earning capacity later in life, with broader costs for society.

Emilie Capes from Randwick has three children under 5. Thomas, 5, is in kindergarten while Josephine, 3, and Charlotte, 2, attend a Goodstart Early Learning long day care centre a couple of days a week.