Sal Khan spends his mornings with his 18-month-old son, and the rest of the day crammed inside a walk-in closet running a school like no other.
"'This location in our house is as far away as you can get from my son while he's screaming' is the simple answer," said the Mountain View, Calif., stay-at-home dad.
Khan, 33, a former hedge fund manager, is the founder and lone faculty of the nonprofit Khan Academy, a collection of 1,800 mostly nine-minute math and science tutorials that include basic addition and organic chemistry. The free videos are anything but flashy, consisting of a doodling electronic pen on a blackboard and Khan's enthusiastic voice.
"There are no bells and whistles," he said. "You just see the concept."
The videos have grown into one of the world's most popular education websites and are watched on average 70,000 times a day.
"I get a sense that it's working because it is so basic," Khan said.
"Students start at 1+1, move at their own pace, pause and repeat videos as necessary. They can do exercises. ... Until they're 100 percent proficient."
He said he got a lot of feedback on how the lessons were set up.
"You feel like you're one of my, younger brother or sister and we're just kind of going over something so it's a very low-stress situation," Khan said.
Indeed, family is what got him started with the online tutorials. Khan started doing the lessons for family members who were struggling with math. He eventually posted them on YouTube so relatives could learn at their own pace.
The videos went viral and grew so fast that Khan quit his job a year ago to run the academy.
Bill Gates and his son are two of Khan's most loyal students.
"There's a website that I've just been using recently with my kids called Khan Academy. ... Just one guy doing some unbelievable 15-minute tutorials," Gates said during an interview at Aspen Ideas Festival 2010.
Google heard of Khan after programmers said their kids used the videos.
Khan students from all around world said the lessons helped them understand difficult concepts.
"He's probably one of the best math teachers I've ever had," French student Charles Eric Edwards told ABC News.
There are plans for the school to grow, thanks to funding from Gates and others but Khan Academy's only teacher doesn't plan to leave his walk-in closet or raise the price.
"We definitely want to make sure we stay focused; that it doesn't ever feel like a large entity that's trying to force information but really is this human interaction," Khan said.