“BY ALMOST any measure, the world is better than it has ever been,” Bill Gates wrote in his 2014 annual letter for the Bill & Melinda Gates Foundation. “People are living longer, healthier lives. Many — though by no means all — of the countries we used to call poor now have thriving economies. And the percentage of very poor people has dropped by more than half since 1990.”

Too few people recognize the progress, Mr. Gates notes, so too few understand how achievable further progress would be. And further progress is needed. More people have entered the middle class than most economists would have thought possible a generation ago, and the ranks of the poor have shrunk even as world population has grown. But more than 1 billion people still live in extreme poverty — on less than $1.25 a day.

Recognizing both the progress and the urgency, the World Bank has set a goal of virtually eliminating extreme poverty across the earth by 2030. In 1990, 36 percent of the world’s population lived in extreme poverty; by 2010 the ratio was slightly less than 18 percent. Even so, World Bank President Jim Yong Kim told us during a recent visit to The Post, the bank and other aid agencies will have to do things differently to accelerate the trend and reach the 2030 goal. One key challenge, he said, is using “precious aid dollars to prepare the ground for private-sector development.”

India, despite its economic progress in recent decades, still is home to a third of the world’s poor. Add in two more countries, China and Nigeria, and you’ve accounted for more than half. But the poorest countries are, like Nigeria, in Africa: Three-quarters or more of the populations of Congo, Liberia, Burundi, Madagascar and Zambia are extremely poor.

Strategies for different countries will differ. Economic growth is essential and, as China has showed, the best anti-poverty tool. As Mr. Kim suggested, such growth requires private-sector participation. But in areas of high inequality, economic growth alone won’t be enough. Aid is essential — and, as Mr. Gates also showed in his letter, aid has been far more effective than public opinion tends to credit.

Over the years, evangelists of various stripes have championed favorite methods to attack poverty: educating more girls, providing microloans to entrepreneurs, building farm-to-market roads. There is no single route. One strategy that Mr. Kim said is proving its worth is conditional cash assistance — giving payments to poor parents who ensure that their children go to school, for example, or get their required vaccinations.

So flexibility matters, but so does determination. The case is pragmatic as well as moral. Mr. Kim pointed to research showing that inclusive growth is good for everyone: Bring up the poorest, and include women and other traditionally marginalized sectors, and the entire economy grows faster. His target, which once would have seemed outlandish, is now quite imaginable. As Mr. Gates writes, “Poor countries are not doomed to stay poor.”