Happy Birthday, HBS!

(Fortune Magazine) -- Does Harvard Business School have a future? Its storied past will get extra attention when the school turns 100 years old on April 8. But in a fast-changing global economy, the world's iconic business school faces new threats of the type that confront all established institutions.

New direct competitors (Beijing University, for example) are gaining appeal. Disruptive competitors, such as corporations that offer faster, better training, are increasing. The market could even see a secular shift in demand if ambitious twentysomethings decide they need a different education for a future right-brain economy based on creativity and imagination.

Since HBS's challenge is faced by many companies, I wanted to find the essence of what has made the place so successful, the core that must remain, no matter what else might have to change. So I asked a varied sample of alumni the same simple question: What's the most valuable thing you learned at Harvard Business School?

"I learned that there are 24 hours in a day, and you can use all of them," says Jeffrey Immelt, MBA '82, CEO, General Electric (GE, Fortune 500).

All their answers are different, but they're all the same: none are about the content of the courses; all are about the experience.

"John Bishop taught production and operations management, and he would test your reasoning and facts through a hypercharged version of the Socratic method that you never forgot. Roberto Goizueta of Coca-Cola (KO, Fortune 500) once said you can think through a problem so hard that you develop a sweat. John Bishop's method taught you to think about business problems that way," says Adrian Slywotzky, MBA '80, partner at management consulting firm Oliver Wyman.

The key words there are "you never forgot." We all forget most of what we learn in school. HBS alumni are no different. What they remember is not the information they were taught but what the experience caused them to realize for themselves.

"Having smart people with different perspectives and expertise working together on tough issues can yield amazingly creative results," says Rick Wagoner, MBA '77, CEO, General Motors (GM, Fortune 500).

It makes sense that the content of the classes isn't what it's all about. That's constantly being commoditized. The professors all write books, available to anyone, and even the famous Harvard Business School cases are for sale.

"I learned that yellowed lecture notes and blackboards filled with algorithms don't teach professionals how to think," says Jeffrey Sonnenfeld, MBA '78, DBA '80, HBS faculty 1980-89; professor, Yale School of Management.

What's extremely hard to copy is the intense experience, which results from the elite nature of the place - plus its brutally competitive system. Bring together the most highly qualified students, then assemble a faculty capable of pushing them beyond where they can comfortably go, and challenge them every day for two academic years. Of course they'll never forget it. But the formula works only if the students and faculty remain exceptional.

One of the best lessons the rest of us can learn from Harvard Business School is that it has kept a self-reinforcing cycle going: it's a preeminent school, so it attracts the best students and faculty, which keeps it preeminent, and so on. As long as that engine keeps turning, HBS will keep delivering the uniquely powerful experience that no one ever forgets - the most valuable thing its alumni take away.

That lesson is important for everyone because HBS's only product is thought; its only capital is human capital. And in an information-based economy, many companies are in the same situation. For HBS, keeping its self-fueled engine going for the past hundred years has been an amazing achievement. Keeping it going for another hundred will be much tougher.