Victor Bastos was making US$20,000 (NZ$25,829) a year as a freelance web developer in Lisbon, Portugal, when he started posting videos to YouTube.
Already fluent in several programming languages and looking to branch into new ones, he thought making instructional videos would help him keep track of what he'd learned.
"It was like an online notebook for myself," Bastos, 33, said. "But then I started getting a lot of subscriptions. People told me, 'Your tutorials are great - why don't you make a full course?'"
Within a few months, Bastos got an email inviting him to do just that.
The proposal came from an online-learning startup he had never heard of called Udemy. The offer: Host his course on Udemy's web-based platform, and he could charge students to take it and keep 70 per cent of the revenues. Udemy would keep the other 30 per cent.
Bastos accepted and got to work fleshing out a full curriculum. His goal: a one-stop course that would turn total rookies into professional web developers.
Bastos started out charging US$49 but soon found that demand for his class was overwhelming and hiked the price tag to US$199 while offering big discounts on Groupon to attract new customers.
The formula has worked - so well that Bastos quit his job to devote himself to teaching on Udemy full-time. Since he began teaching 'Become a Web Developer From Scratch!' in late 2011, it has drawn some 7000 students.
In that time - a year and a half - Bastos has earned US$452,985.70 (NZ$584,800.74).
He is not an outlier. Udemy, launched in 2010, reports that its top 10 instructors have generated more than US$5 million in revenue so far.
Many others are taking in sums that would be unheard of for a high school teacher and impressive for a university professor.
A class on IT certifications and training has earned its teacher US$260,000 in a little less than two years.
One on video, animation, and multimedia has brought in nearly US$150,000 in the same period.
The focus is on technical skills, and computer classes are the biggest draw. But Udemy's 8000 offerings also include a smattering of courses in the humanities, social sciences, and other subject areas. A yoga instructor named Dashama has earned some US$45,000 in her first 11 months.
Unlike schoolteachers and professors, Udemy instructors don't need credentials, and you don't have to quit your day job to get started.
The Silicon Valley start-up says most publish their first course within two to four weeks, then spend an average of five to 15 hours per month updating course materials and responding to students' questions.
They receive some initial support from Udemy and share tips on best practices, but they can craft their own curriculum and teach basically whatever they want.
The company is quick to point out that it's not a get-rich-quick scheme: The average instructor on the site has earned more like US$7000 in total, and only a minority quit their day jobs.
"You don't start teaching purely for the money," Udemy spokesman Dinesh Thiru told me. "You start teaching because you're passionate about something."
That said, the site is set up to give top billing to its most highly rated classes, which means that popular instructors have a chance to reach large numbers of students - and reap the rewards.
That open-marketplace model is in contrast to similar sites like Lynda.com, which produces its courses in-house and sells them via membership rather than a la carte.
When I first heard of Udemy, I mentally lumped it with the MOOCs - massive, open, online courses - that have sprung up in great numbers in the past two years.
These include Coursera and Udacity, the rival for-profit start-ups launched by Stanford professors, and EdX, a nonprofit that started as a collaboration between Harvard and MIT. In fact, Udemy stands apart.
The courses are not free, the teachers are not affiliated with universities, and the lectures and course materials are served on-demand, rather than by semester.
If the MOOCs are disrupting higher education, as the cliché has it, Udemy is aiming to disrupt something less grandiose - night schools, perhaps.
In general, online lectures fall short of a full classroom experience, and I've argued in the past that the MOOCs are better seen as a replacement for textbooks than a replacement for university as a whole. By those lights, Udemy and its kin could be viewed as a 21st-century hybrid of the how-to book and the professional development seminar. Or maybe an Airbnb for career skills instead of accommodations.
Cynics might wonder if Udemy courses are a rip-off, since one can often find similar material for free elsewhere on the web. Codecademy, for instance, offers a free interactive crash course for computer-programming newbies that covers some of the same ground as Bastos.
On the other hand, Codecademy's automated lessons lack the human touch of Bastos' homespun lectures. And Bastos tells me he prides himself on promptly answering all his students' questions, which is not something you'll find on a free YouTube channel.
Besides, the cost is hardly exorbitant, particularly given how valuable programming experience is these days.
If I have any concern with Udemy, it's the risk that it may overpromise and underdeliver in some cases, not only for its students but for its teachers.
Bastos may not have credentials, but he possesses both an extremely marketable knowledge base and an obvious knack for online teaching.
Not everyone shares that combination, and those who don't may find themselves overmatched and undercompensated if they try to replicate his success.
Udemy will also need to make good on its pledges of quality control in order to assure students that their money won't go to waste.
Then again, the same could be said of professional development seminars - and Udemy has the advantage of a user-rating system to separate the good courses from the bad.
"If the instructor isn't up to snuff - if something fell through our gaps - it's quickly pointed out by the students," Thiru said, "and that course is not going to be very visible on Udemy in the future."
Forget get-rich-quick, then. The opportunity that sites such as Udemy offer is better summed up as get-rich-if-you're-really-good. It's not such a novel concept in most fields - just rather unusual for education.