For five months, Nicolas Philibert visited more than 100 single-class schools in his native France to find the perfect setting for his documentary, "To Be and To Have" (2002). He sought an amiable teacher, children from pre-K through fifth grade learning together in the same room, large windows for ample lighting, and bucolic views.

Georges Lopez, who taught in rural Saint-Étienne-sur-Usson for decades, is the fatherly mentor everyone had—or wished they had—as a child. With Mr. Lopez's guidance, 13 students tackle far more than conjugations and geography: They learn how to talk about a parent's cancer, when it's best not to tattle on peers, how to flip a crepe, and what to do when family members offer different approaches to a single math assignment.

Philibert's earlier works successfully looked at mountaineering, a psychiatric hospital, and the Louvre's secret life after hours. But the appeal of "To Be and To Have"—the top-grossing French documentary of all time ($9.5 million)—has been remarkable.

On Jan. 3, it received yet another award for best documentary, this time from the National Society of Film Critics. It's still playing in select theaters around the US. The veteran filmmaker discussed "To Be and To Have" via phone from his apartment in Paris.

What were your own primary school days like?

I grew up in a city, not in the countryside. As a kid, I hated going to school. During primary school, my parents had to put me in a different school every year. Making this movie gave me the opportunity, for the first time of my life, to be happy in school.

Why did you choose to film a single-class school?

The mix of ages was very interesting to me because it generally translates into solidarity between the kids. The older ones take responsibility for the younger ones. Today, we live in a fenced-up world where generations don't talk to each other, where individual success and the cult of money have become supreme values. In addition, I really wanted to film in the countryside, to film nature, the seasons, time going by.

Some of the students, such as Jojo [a small boy whose attention often wanders], are given much more time on screen than others. Was he actually the dominant personality in the class?

It's true that Jojo is very present in the movie. He was funny, a bit mischievous, and very spontaneous. But the movie also shows children who are more shy, more discrete, more secretive. During the editing, I had to find a good balance.

Do you go to screenings to see how audiences react?

I rarely go see my movies. But I very often participate in debates with the public at the end of the screening. The movie leaves a lot to people's imagination. Everybody reacts to it based on his own experience, past, personal memories from school. I had the opportunity to travel with the movie to a number of French cities. But also abroad, in Japan, Korea, Italy, Switzerland, Brazil, Canada, the United States. It was extraordinary to see that the movie could touch spectators from different cultures and languages.

Why do you think it resonates with so many people?

The movie has a universal dimension. The real subject is growing up. It's the learning of life. It comes from the desire for a harmonious world, where conflicts would be resolved peacefully, where children would learn to respect each other and to respect themselves, where everybody would slowly gain self-confidence and find the way to his own future.

Do educators react differently?

Most educators saw the movie as an homage to their beautiful and difficult profession. They have often compared their own experience with what they saw on the screen, sometimes to criticize the methods of this teacher that they found too traditional, or too this, or too that. But in general, their reactions were warm.

Do you have ideas about featuring another side of education in a future work?

I don't have any intention to become specialized in education matters. Nevertheless, all my movies, explicitly or not, revolve around the question of how to live together.