Sal Khan's first inkling that COVID-19 was going to disrupt education around the world came in February, when the popular online learning platform he created saw a surge in traffic from South Korea.
"We got a letter from a teacher who was saying how they were using Khan Academy to keep the kids learning during school closure," he told AFP from San Francisco, saying he soon realized the vital role his organization could play in the pandemic.
The idea for Khan Academy began in 2004 when Khan, then a hedge fund manager, started giving math lessons to his 12-year-old cousin who lived on the other side of the United States, using Yahoo Doodle.
Since that time, it has become one of the world's leading internet education sites, available in 46 languages with a user base of 100 million, for whom it is completely free, thanks to the support of the Gates Foundation, Google and more.
But Khan soon recognized that the platform's videos, articles and online tests designed to supplement students' learning in normal times weren't enough for quarantined schooling.
They began creating detailed daily schedules to provide children with the structure they were missing out on in schools, and hosting webinars to help parents and teachers.
"We also began stress testing the servers," added the 43-year-old, as the number of learners shot up from about 20 to 30 million per month, and each user spent two-thirds more time learning than previously.
- 'Pull kids out of the screen' -
As many students return to school only via virtual or hybrid learning this fall, Khan said that the world had to find ways to mitigate the impact.
His tips include giving children a dedicated workspace that helps them mentally differentiate where they're studying and where they can goof off.
Another suggestion to reduce feelings of isolation: physically-distanced park meet-ups between families with children of a similar age.
In order to prevent mental atrophy and prepare their kids to return, parents can leverage online learning for the core subjects like math.
"Try to get at least 20 to 30 minutes of practice in a day," he said.
For reading and writing, parents can look for book lists and organize Zoom meetings for their children to talk about what they read. They can also write about the books and have their peers give feedback.
"You've got to make it interactive, you've got to pull kids out of the screen, a lecture over Zoom is not a good idea," he said.
One drawback of distance learning is that it widens the attainment gaps between children from better and worse-off families.
Khan admitted the situation was far from ideal, but said in the long run there may be certain "silver linings" -- such as renewed effort to close the digital divide.
A project he's currently working on called "schoolhouse.world" would connect children to tutors online for free.
- Leveling the playing field -
Unlike other major online education players like Coursera and EdX that are fee-charging, nonprofit Khan Academy teaches subjects from kindergarten up to college level at zero cost.
Khan, who studied computer science at MIT and has a Harvard business school MBA, devised many of the site's courses himself, particularly in math and science (it also hosts subjects like history, economics and law).
He is widely praised for instilling a sense of wonder about a subject, while also explaining the nitty-gritty in ways that are clear and help build confidence.
Multiple studies have found use of the platform is linked to higher test scores, particularly in math, and Khan Academy has established partnerships with school districts across the US.
Most recently, a small randomized controlled trial by UMass-Amherst this May found the free literacy app Khan Academy Kids boosted early literacy skills among high-poverty families.
How did he become such a proficient teacher?
"I was the kid who wanted to learn for learning's sake," he jokes, rather than studying for the test.
When word of his early success tutoring his cousin Nadia got out among his large family, more cousins came to him for help, and "I was just trying to explain to my cousins, and I guess everyone's cousins, the way that I learned myself," added Khan, who is of Indian and Bangladeshi descent.
In 2015, Khan Academy became an official partner of the SAT -- the standardized test used for US college admissions.
Here too, the platform's impact on outcomes has been backed by research, unlike for-profit companies that charge up to thousands of dollars for the same services but don't publish their efficacy data.
This, Khan said, went to the core of his philosophy: that education isn't well suited to the marketplace and it's his job to "level the playing field."
"If there's a young child who needs to learn, we shouldn't be saying, 'How much do their parents make?' Or 'Can they get the credit card out?' We should say, 'Let's teach them.'"