So his parents let him drop out. Instead, Karp embarked on a homeschooling regimen with the help of several tutors, learned to speak Japanese and pursued his digital interests with abandon.
"He needed the time in the day in order to create," said Ackerman, who divorced when her son was a teenager. "And that's what he is. He's a creator."
Just shy of his 18th birthday, Karp boarded a plane to Japan and lived there for several months alone, running technology for the parenting site UrbanBaby. Then he moved back in with his mother, dabbling in various digital startups for several years before alighting on the idea of creating his own blogging platform.
"David would come running through the apartment saying, 'Mom! Mom! There's this and this and this!'" Ackerman said. "And I didn't know what the heck he was talking about. Because it was a whole other language."
Tumblr stands out for a creative layout that enables users to easily share blog posts, photos and video with one another in a mosaic of interlocking information.
Mayer said she knew Karp had to be a good guy even before she met him. She could tell by Tumblr's elegant look and simple tools for creating content.
"With clothes or art or design, you can always tell if the person who made it is nice," Mayer said. "When you use Tumblr, you can tell there are a lot of empathetic people who understand what makes a person feel good, what makes a person feel safe in terms of sharing their work."
But as popular as Tumblr has become, the service remains unprofitable. And the company has had its share of stumbles.
In April, Karp announced in a blog post that Tumblr was laying off its team of journalists and editors assigned to cover the "living, breathing" Tumblr community.
After hundreds of stories and videos, he said, Tumblr's experiment "has run its course for now, and our editorial team will be closing up shop and moving on."
The insensitive handling of the news prompted its fair share of Internet jabs at Karp.
The New Yorker magazine, for example, published a humorous piece called "The Collected Messages of David Karp." It included a would-be Christmas card from the Karp family in 2023, informing David Jr. that there is no Santa Claus.
Advertising has been a missing ingredient because Tumblr, like many online services in their early stages, focused on building a loyal audience before turning its attention to making money. That's why the Yahoo deal is so pivotal for Karp and his small team of creative thinkers.
For now, though, they're basking in the glow of joining forces with an Internet behemoth. As for Karp's mother, she was positively giddy at the prospect of meeting Mayer on Monday night.
"I'll get to talk her ear off about how wonderful David is," Ackerman said. "That's what moms do."
Associated Press writers Barbara Ortutay and Michael Liedtke contributed to this report.
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