Fixes looks at solutions to social problems and why they work.

Have you thought of a clever product to mitigate climate change? Did you invent an ingenious gadget to light African villages at night? Have you come up with a new kind of school, or new ideas for lowering the rate of urban shootings?

Thanks, but we have lots of those.

Whatever problem possesses you, we already have plenty of ways to solve it. Many have been rigorously tested and have a lot of evidence behind them — and yet they’re sitting on a shelf.

So don’t invent something new. If you want to make a contribution, choose one of those ideas — and spread it.

Spreading an idea can mean two different things. One is to take something that’s working in one place and introduce it somewhere else. If you want to reduce infant mortality in Cleveland, why not try what’s working in Baltimore?

Well, you might not know about what’s working because there’s no quick system for finding it.

Even when a few people do search out the answer, innovative ideas don’t spread by themselves. To become well known, they require effort from their originators. For example, a Bogotá, Colombia, maternity hospital invented Kangaroo Care — a method of keeping premature babies warm by strapping them 24/7 to Mom’s chest. It saved a lot of lives in Bogotá. But what allowed it to save lives around the world was a campaign to spread it to other countries.

The Colombians established Fundación Canguro and got grants from wealthy countries to bring groups of doctors and nurses from all over to visit Bogotá for two or three weeks. Once the visitors had gone back and set up a program in their hospital, the foundation loaned them a doctor and nurse to help get them started. Save the Children now leads a global partnership to spread Kangaroo Care, with the goal of reaching half the world.

In short, this work requires dedicated organizations, a smart program and lots of money.

The other meaning of spreading an idea is creating ways to get new inventions out to people who need them.

“When I talk to college students or anyone who’s thinking about entrepreneurship or targeting global poverty, the gadget is where 99 percent of people start thinking,” said Nicholas Fusso, the director of D-Prize (its slogan: “Distribution is development”). “That’s important — but the biggest problems in the poverty world aren’t a lack of gadgets or new products. It’s figuring out how people can have access to them.” So D-Prize gives seed money, in chunks of $10,000 to $20,000, to tiny new organizations that have good ideas for how to distribute useful things.

This analysis may be familiar to regular readers of Fixes. Indeed, the first Fixes column, more than five years ago, focused on distribution: getting health care to people in rural Africa by putting health care workers on motorcycles and keeping the bikes running.

Fusso likes to use the example of malaria. The modern insecticide-treated bed net was invented in 1980, when one million people a year — the vast majority small children — were dying. What impact did the invention itself have? None at all, at first. Deaths each year rose gradually, and then rose sharply — to a peak of 1.8 million in 2004, when they began to fall.

What happened then? The world finally started putting money into fighting malaria, including distributing bed nets. Today, deaths from malaria are one third of what they were in 2004.

The invention was crucial, of course — but it was distribution that gave it impact.

Also in 2004, a French researcher named Pascaline Dupas, working in Kenya, was talking to a Kenyan colleague who was running to give some money to her high school-age sister. “These girls have no money, and I don’t want her to end up with a sugar daddy,” the colleague said.

“But that’s crazy!” Dupas replied. “Doesn’t she know she could get H.I.V.?”

Perhaps she did know, but the vast majority of girls in Kenya did not. The assumption was widespread that someone relatively wealthy and established was unlikely to have the virus. Three quarters of 15-year-old Kenyans surveyed thought teenage boys were more likely to be infected than men over 25.

This was very wrong. H.I.V. rates were six times higher in men aged 20-24 than they were in boys 15-19, and the rates rose with each additional year of sexual activity.

Across the world, but especially in high-poverty countries, many high school girls look for boyfriends who are five to 10 years older, because those men have sophistication, stability and money. These sugar daddies give the girls gifts, pick them up from school in nice cars, pay their school fees and even help their families.

Moreover, girls are much more likely to have unprotected sex with a sugar daddy than with boys their own age. The power imbalance in the relationship makes it difficult to insist on condom use. And avoiding pregnancy is less important to them, as wealthier and more stable men make better husbands and are more likely to marry them than teen boys are.

Sugar daddies were one big reason that the H.I.V. rate for teenage girls in Kenya was five times higher than for teenage boys. Dupas wondered if simply providing the girls with correct information about the relative risks could change things.

She designed a 40-minute lesson to help girls in eighth grade (average age: 15) to understand the H.I.V. risks associated with sugar daddies. It started with a 10-minute video. Then a facilitator from a local civic group showed statistics about actual infection rates by age and gender. The class discussed the reasons for these patterns, and gradually came around to talking about sugar daddies.

This training was tested in 328 schools in western Kenya against the country’s standard school anti-AIDS curriculum, which promoted abstinence. Dupas’s message was very different: “Your risks are far less if you choose a partner your own age.”

“It made us very popular with the young boys in the class,” she said.

The next year, Dupas counted how many girls had become pregnant, and recorded the fathers’ ages. The group that heard Dupas’s lesson had a pregnancy rate 28 percent lower than those who received the standard abstinence-based curriculum. And their rate of child bearing with men five years or more their senior was 61 percent less.

Dupas didn’t have money to do H.I.V. testing, so she didn’t study the effects on H.I.V. incidence. But pregnancy is likely a good stand-in for unprotected sex, and therefore H.I.V. infections.

For a 40-minute single intervention at negligible cost, it was a stunning impact.

And then — nothing happened. One organization tried to replicate the study in Cameroon, but didn’t collect the right data. Dupas submitted the paper to various journals, finally publishing it in the American Economic Journal in 2011. Still, nothing happened — perhaps because people who design anti-AIDS programs don’t usually read economics journals, she said.

Related More From Fixes Read previous contributions to this series.

Finally, someone ran with it. But it was only because a young American, Noam Angrist, had studied at M.I.T. with Esther Duflo, a professor who was Dupas’s mentor. Angrist had also worked at J-PAL, a laboratory Duflo helped to establish to carry out scientific studies of anti-poverty programs.

In 2013 Angrist was living in Botswana, which has the second-highest H.I.V prevalence of any nation — 45 percent of 40-year-old men. With some friends, he did some small experiments to see whether the same misconceptions about sugar daddies existed in Botswana as in Kenya. They did. “When we showed them the actual graph, they would physically gasp,” he said. Young1ove was in business.

The new organization quickly won $20,000 from D-Prize and formed a partnership with Evidence Action, a new organization that seeks to scale up proven inventions. So far Young1ove has taught the mini-course — adapted for Botswana — to 35,000 youths, operating in a third of Botswana’s schools. As the program grows, a study is comparing schools that have it — taught two different ways — to schools that don’t yet, to test both the program’s impact and whether teachers or youth facilitators get better results. The organization is also carrying out small pilot programs in South Africa and Zimbabwe.

Earlier this month, Young1ove and Evidence Action won a $700,000 grant from the new Global Innovation Fund, whose donors are the overseas development agencies of the United States, Britain, Sweden and Australia, and the Omidyar Network. The prize money will go to finishing the study and, if the results are good, rapid growth.

Young1ove is the largest of at least three groups trying to distribute Dupas’s curriculum. Jeunes Braves is working in Togo, and Power2Girls is starting in Ghana. Both won D-Prizes as well.

Organizations like J-PAL and Evidence Action’s parent, Innovations for Poverty Action, are sometimes called the Randomistas, because they do randomized control trials. They’ve led a shift in anti-poverty work toward using scientific studies to see what’s effective. “In the last seven, eight years, we’ve moved away from ‘it’s all about the talented individual’ to ‘it’s all about the impact,’” said Gabriel Broadbar, director of the New York University Reynolds program in social entrepreneurship (which runs its own mini D-Prize).

The Randomistas have identified programs that work well and cheaply: bed nets, school-based deworming to rid children of parasites, installing chlorine dispensers at village taps, among others. The logical step now is to scale them up.

This is what Evidence Action tries to do. Karen Levy, the group’s director of global innovation and beta, said that the challenges differ greatly from those of inventing something new: How do you fit the program into a country’s policy and regulatory framework? What’s a sustainable business model? How do you make it easy for lots of people — not just your original staff — to do well?

She used the example of deworming. “Rather than send people to every single school, how do you design trainers of trainers in a cascade so it can be delivered by tens of thousands of teachers with the same results?” she said.

Philanthropists and government aid agencies are only starting to get interested in the challenges of distribution — one new philanthropy that does have this focus is Good Ventures. As for academia, it still rewards invention almost exclusively. “There’s a lot of attention and award-giving and prize-giving and credit to people who come up with fancy new ideas instead of reaching people and having impact,” said Brodbar. “The incentives aren’t aligned. The culture of social entrepreneurship needs to change.”

Recognizing the true value of spreading an idea would also allow people who aren’t inventors (which is most of us) to get involved in social change. “The notion that if you want to engage in [social entrepreneurship] you have to have the big idea does a disservice to this space and people who want to play a role in it,” said Brodbar. “It’s a much wider front door.”

Join Fixes on Facebook and follow updates on twitter.com/nytimesfixes. To receive e-mail alerts for Fixes columns, sign up here.

Tina Rosenberg won a Pulitzer Prize for her book “The Haunted Land: Facing Europe’s Ghosts After Communism.” She is a former editorial writer for The Times and the author, most recently, of “Join the Club: How Peer Pressure Can Transform the World” and the World War II spy story e-book “D for Deception.” She is a co-founder of the Solutions Journalism Network, which supports rigorous reporting about responses to social problems.