On May 31, 2012, David McCullough Jr. was “just a regular high school English teacher.” But by June of that year, he was regular no more. His email inbox was flooded with messages from around the world, television trucks appeared in his driveway, and Charlie Rose interviewed him for his CBS show.

On Tuesday of this week, while sitting on the porch of his Oak Bluffs home, Mr. McCullough reflected on the surprise turn of events that took place just over two years ago. “I’m well into middle age, and mild mannered, and heavily vanilla. It’s not the formula for renown.”

Yet people all over the world remain captivated by him, all because of a commencement speech he delivered two years ago at Wellesley High School. On June 1, 2012, he stood in front of the graduating class, a group of students he knew well and cared for deeply, and told them “you are not special.”

Taken out of context, the message sounds “hectoring and almost like heresy,” said Mr. McCullough. “But it was really just a playful teasing, beginning as a way of setting up the more important points that come at the end.”

Indeed, the meat of Mr. McCullough’s speech is encouraging and reflective. As both a veteran teacher and a parent of four, Mr. McCullough has a prime vantage point on today’s teenagers. On that June afternoon he thought he was sharing his words with just the Wellesley High community. But the speech was filmed by someone in the audience and shared on YouTube. It quickly went viral and has been watched by over two million people. Recently, Mr. McCullough elaborated on the speech in a book, published this April, entitled You Are Not Special, and Other Encouragements.

The book’s 10-page pitch was actually drafted while Mr. McCullough was on the Island two summers ago. The Island is his family’s summer escape, but his roots here lie much deeper. He is the son of historian David McCullough, and had been a year-round resident since early adolescence. His mother’s side of the family first came to the Island in the mid 1800s. On Tuesday evening, only hours after driving off the ferry, Mr. McCullough visited Bunch of Grapes for an author event.

The book, targeted for a teenage audience, and, in fact, dedicated to them, offers advice on how to live life for its simple joys, not for the shiny allure of trophies and medals, certificates and accolades.

Over the last decade or so, Mr. McCullough said he has noticed two major changes in the attitudes of his students. One is the eagerness to appear impressive, especially to college admissions officers. The other is the sense of narcissism promoted by the avalanche of new technology and social media.

“They’ve come to see admissions to one of these prestigious schools as a referendum not just on their quality as a student, but on their quality as a human being,” said Mr. McCullough. “And that, to those of us charged with their education, is kind of a concern.”

The purpose of studying, he said, should be learning about the world, not gaining material achievement, but it’s just not that way anymore. And with technology making kids long to constantly broadcast everyday experiences to their entire network of friends, the idea of prolonged concentration is almost laughable.

That’s a shame, Mr. McCullough said, because “anybody will assure you that significant work requires full investment and sustained dedication.”

But Mr. McCullough is not one to believe that kids are entirely responsible for this shift.

“Educated people are getting married later and they’re having fewer children, which means that they’re further along in their careers and they have more resources to expend on fewer children,” he said. “And so the stakes are higher for the parents on the success of those children, and kids feel that pressure.

“It’s more than just trying to keep up with the Joneses,” he added. “It’s let’s put the Joneses in the dust.”

Though changing this attitude is by no means a simple undertaking, he has faith that it is possible.

“Kids should embrace challenges, should dive into interests and not worry about how they’re going to look if things don’t go smoothly,” he said. “Play the game because you love to play the game . . . and good results will surely follow.”

And to parents?

“I think parents should take a step back and remind themselves that their children’s responsibilities are their children’s responsibilities. . . at some point the training wheels need to come off.”