This year I went to my high school class reunion. It was a hard thing to face for me and, apparently, for a great many of my classmates as well. Three quarters of them didn’t show up. It’s an indication of the extent to which we all regard our past as a guilty secret, and those who have shared it as people to be avoided.

Now just imagine that your past had been shared in documentary form with millions of others. That is the fate of Michael Apted’s subjects in “49-Up.” Every seven years since 1964, he has come back to profile the same group of people his camera first encountered when they were 7 years old. Now they’re 49. Not many of them have welcomed his return.

In fact, like my high school classmates, many are refusing to participate. But let me take this opportunity to say a big thank you to those who, however reluctantly, are still allowing Mr. Apted to pry into their lives. For the 7-Up series looks with each installment more and more like one of the most remarkable cinematic projects there has ever been.

This is not only because of the intrinsic interest of the life stories it tells. Even more interesting are the reflections in those stories of slow-moving changes in our world that we might not otherwise notice.

One of these is in the premise of the series itself, which clearly owes its existence to a typically 1960s and British obsession with social class. Now that titanic mid-century struggle looks ever more like a non-event, while its familiar social divisions have given way to a unitary and postmodern celebrity culture. As one of these 49-year-olds says, the series now looks like a reality show long before there were such things.

The 7-Up series was set up as a serious social experiment. Equal numbers of privileged and underprivileged children were chosen with a view to showing, as the years rolled by, how the British class system operated to exalt the former and cast down the latter. Instead, as the years rolled by, class became an ever-diminishing factor in their lives and in their worlds.

Now Tony, the East End cockney who became a cab driver, has a lovely suburban villa in Essex but is semi-retired and spends most of his time at his holiday home in Spain. Sue, another cockney who went on to become a secretary, is now an administrator at London University and looks forward to retiring to Cornwall with her second husband, Glen. She says she feels as if she has moved into the upper classes.

Meanwhile Neil, a bright lad from Liverpool who went to university but dropped out, is still battling depression and living on government assistance, as he has done for nearly the whole of his adult life. Bruce, shown at age 14 saying that at the posh St. Paul’s School “they didn’t enforce being upper class,” studied mathematics at Oxford and then taught in the East End of London and in Bangladesh.

But having married late and started a family in the last seven years, he is now a defiant sell-out, teaching at the private St. Alban’s School, where the work is so much more satisfying and the pupils of a much higher academic level than in the East End. When he was teaching there, he says, he thought his good influence would act on his pupils like water dripping on a stone. Instead the water drip of their academic dullness and indifference wore him away.

Looking at the original film now, he can hardly recognize himself at age 7. That child looks so lost to him. Cue his 7-year-old self at boarding school saying to the camera: “My heart’s desire is to see my daddy” — who was 6,000 miles away. He is surprised to be so happy and content all these years later.

Generally speaking, the focus of the films has shifted from work and money and social class to marriage and family. What unites these people across their class boundaries, making all other considerations seem minor — and what moves us again and again about “49-Up” — is their still undimmed wish to be happy in love.

For a surprising number, the wish has come true. Next to Tony, the most attractive is Suzy, the upper-class girl who is shown again — as she has been each of the last four films — looking morose and chain-smoking at 21, telling the camera that she was very, very cynical about marriage and children, and then, seven years later absolutely transformed into a lovely and radiant young woman.

“What happened to you?” the Michael Apted of 21 years ago asks. The answer was Rupert, her husband, to whom she is still happily married and on whose account, perhaps, she seems to grow prettier and younger-looking with each new installment. She tells us that, with this film, “For the first time I actually feel happy in my own skin.”

Suzy’s beauty and charm make all the more regrettable her confession that being interviewed for these films is “very difficult, very painful, not pleasant in any way.” She adds: “This is me. Hopefully, I shall reach my half century next year and bow out.”

Everyone who expresses an opinion on the subject seems to feel the same way. “Every seven years a little pill of poison,” one says. Moreover, Mr. Apted himself is now 65. How much longer can the series continue? Let’s hope that, out of public-spiritedness and in spite of their dislike of it, those charming 7-year-olds in 1964 will soldier on, cinematically, at least until they reach the biblical three-score and 10.