Bill Gates says they have accomplished "a lot, but not as much as either of us would like."
While the foundation has had considerable success with international initiatives, their work towards their biggest domestic cause has been less fruitful than they had anticipated. For instance, their eponymous foundation has spent billions on vaccination initiatives for children in developing nations, which has lead to a decrease in diseases like polio and malaria and an increase in child life expectancy.
"We've spent $15.3 billion on vaccines over the past 18 years. And it's been a terrific investment," writes Melinda. "Better immunization is one reason why the number of children who die has gone down by so much, from almost 10 million in 2000 to 5 million last year."
When it comes to improving the American education system however, the powerful couple has seen less quantifiable evidence that their investments are paying off.
"Unfortunately, although there's been some progress over the past decade, America's public schools are still falling short on important metrics, especially college completion," writes Bill. "And the statistics are even worse for disadvantaged students."
The Gates have been giving to American education initiatives since 2000, and according to data from the National Center for Education Statistics, the 6-year college graduation rate for American college students has hovered around just 60 percent for decades.
Broadly, the couple has expressed that their primary domestic goal is to address educational inequality for students of color and low-income students, but achieving this objective has proved more difficult than they expected.