By David Cameron and Jeffrey Sachs

In Koraro in Ethiopia, a dozen or so young women gathered at the primary school to describe their progress as the first girls from their village at the secondary school in the next valley. With beaming eyes, soft voices and determination, each described how she would soon return to the village as a teacher, or plumber, or electrician, helping to create new jobs and bring new prosperity.

An hour earlier, their fathers had nearly burst with pride as they described the reality of these young women's education. If it takes a village to raise a child, it is also true that one child can inspire a whole village.

Koraro is a Millennium Village, powerfully demonstrating how an impoverished rural community, through its own efforts and just a little help from the outside, can lift itself out of grinding poverty. The community's future now rests with the coming generation of skilled young women who will teach in the new schools, create new jobs and improve the local harvests.

Sustainable development is a cumulative process. The first young women graduating from school are already inspiring the 12-year-old girls who will soon follow in their footsteps. They will marry later, have fewer and healthier children, and send their own children to school.

Koraro is powerful evidence of how women can hold the key to development in some of the world's poorest countries – in education, enterprise, micro-finance and healthcare. Investing in women pays dividends throughout the entire community. So how can we put women at the heart of our vision for international development?

First, the UK needs to meet our moral commitment to increase spending on aid to 0.7 per cent gross national income. But this investment has to go hand-in-hand with greater transparency, ensuring the money reaches the people who need it most. A Conservative government will create an independent aid watchdog and publish every item of aid spending online, so that the performance and impact of development policies are transparent to taxpayers in Britain and to people in the developing world.

Second, with women making up a significant majority of the world's poorest people, we need targeted action to support women the world over. Take maternal mortality, for example: 350,000 women die during childbirth every year, a figure that has barely fallen in the past two decades in many regions. A Conservative government will work to strengthen health systems and family planning facilities in developing countries, including steps to improve access to well-trained midwives and emergency obstetrics care.

Third, because a joined-up international approach is essential, we need to ensure that action on women and development is on the agenda at key global meetings. A Conservative government will make this a top priority for Britain at the G8, G20 and UN summits this year. And it will work closely with countries such as Canada and the US, which have already said that tackling maternal and child mortality should be an urgent global priority as part of achieving the Millennium Development Goals.

The Big Society is about bringing together the global community as much as it is about building stronger local communities. We will not stand by while eradicable disease and poverty continues to blight our world – and will make sure the money and the policies are in place to make a lasting difference.

Jeffrey Sachs is director of the Earth Institute, Columbia University, and author of 'Common Wealth'; David Cameron is leader of the Conservative Party