“I wanted to yell at them: ‘God, chill out!’ ” she said.

Years later, when Santos became a psychology professor at Yale University, she noticed that her students seemed to be neglecting the latter. Their academics were solid (there was a reason they had been accepted to Yale), but the amount of pressure they put on themselves was wrecking their stress levels, their mental health, their sleep, and, ultimately, their happiness.

NEW HAVEN — When Laurie Santos was growing up in New Bedford, her mother was a high school guidance counselor, which meant Santos got lots of good advice about school as well as about life.


Instead, she created a class for them, one that is now the most popular in the history of the 317-year-old Ivy League school.

The course, Psyc 157, is titled “Psychology and the Good Life,” but everyone at Yale calls it “the happiness class.” Some 1,200 students enrolled when the course was unveiled this semester. That is nearly a quarter of Yale’s undergrads.

The story of how Santos, 42, transitioned from studying how nonhuman primates interact — her research specialty — to undergrad happiness began in earnest two years ago when she became the head of Silliman College, one of 14 residential houses at Yale.

She and her husband moved into an apartment at the college, and Santos found herself assuming the role of den mother to nearly 488 students, many of them making the mistake of thinking they will find happiness in external circumstances. Getting a good grade, the evidence showed, would not change unhappy.

“So I brought together work on positive psychology and behavior change, then put it into an applied form to create the class,” Santos said. “The goal was to rewire the way the students viewed the pursuit of happiness.”

The success of the class has been unprecedented. So many students signed up that the meeting space had to be moved to Woolsey Hall, a cavernous, cathedral-like auditorium typically used for things like symphony concerts. The sheer volume of students requires two dozen teaching fellows.


Jennifer Chen, left, and Sean Guo laughed during their "Psychology and the Good Life" class in Battell Chapel at Yale University. Monica Jorge/The New York Times

The twice-weekly lectures straddle the line between a traditional psychology class, with dives into notable research, and a self-help seminar, with “psych pro tips” and “rewirement requirements,” assignments for breaking bad habits or creating good new ones.

Her most talked-about assignment came earlier this semester when Santos taught the students about “time affluence” — the opposite of their usual “time famine” — by surprising them with the news that there would be no class.

They were ordered to use the unexpected free time creatively. No work. No studying. Put down your phones. Do something together.

“Two students in front of me just started crying,” she said.

Students went in groups to campus museums they’d never entered. They made new friends. And then Mother Nature extended the experiment. A snowstorm was on the way, and Yale canceled school for the following day. Many of the students stayed together all through the night.

“We know from psychology that the top key to happiness has to do with intentional social interactions,” Santos said. “Very happy people spend time with other people.”

Santos’ teachings are now going beyond the walls of Yale. A Santos-led course called “The Science of Well-Being” is available on the website coursera.org, complete with video lectures and reading assignments. In the month since it’s been available, a Yale spokesman said, it has been taken by 78,000 people in more than 168 countries, making it the most popular online course launch in school history.


But getting the information out there is one thing. Absorbing it in a way that changes behavior and thinking for the better is another thing entirely. Santos calls it “the GI Joe Fallacy,” after the 1980s cartoon.

“GI Joe always said: ‘Now you know, and knowing is half the battle.’ That is simply not true,” she said.

She said recent research suggests that simply knowing something — how to be happy, for instance — is a shockingly small part of the mind’s battle to make decisions that lead to happiness.

“You have to set up better situations,” she said. “You don’t get it for free just by knowing something.”

To that end, she said she tries to practice what she preaches. And, she said, she fails often. (Her husband jokingly documents her failures.)

On a recent afternoon, Santos’ students gathered in Woolsey Hall for lecture No. 18, this one focused on being “slaves to our habits,” which addressed the use of positive cues as a way to hack those habits for a huge impact on behavior and happiness.

As Santos prowled the grand stage, wearing a wireless mic, with a huge screen behind her and an audio/visual tech running the show from the back, it was more TED Talk than traditional lecture.

Some students took diligent notes. Others stared off into space or their phones. But perhaps most notable was who wasn’t there. About 1,000 students.


Only about 200 undergrads had shown up for the lecture. Attendance, students in the class said, had fallen dramatically after their mid-term exam.

Where were the rest? Maybe they were practicing time affluence. Perhaps they were working on their final project, which is to implement an intervention — such as regular meditation — and then write about it.

Or maybe they had finally accepted the fact, as Santos had told them, that good grades would not make them happy.

Billy Baker can be reached at billybaker@globe.com.