From Wikipedia

Seven Up Series

Episode Four

Seven Up - Twenty Eight

The series has received extraordinary praise over the years, the epitome of which may be Roger Ebert's comments that it is "an inspired, even noble, use of the film medium", that the films "penetrate to the central mystery of life", and that the series is among his top ten films of all time. Attempts have been made to repeat the series with subjects in the United States, the Soviet Union, Japan, and South Africa. In a list of the 100 Greatest British Television Programmes drawn up by the British Film Institute in 2000, voted for by industry professionals, 28 Up was placed 26th. The series has also been satirized; The Simpsons' 2007 episode "Springfield Up" is narrated by an Apted-like filmmaker who depicts the past and current lives of a group of Springfield residents he has revisited every eight years.

The original hypothesis of 7 Up was that class structure is so strong in the UK that a person's life path would be set at birth. The producer of the original programme had at one point thought to line the children up on the street, have three of them step forward and narrate "of these twenty children, only three will be successful" (an idea which was not used). The idea of class immobility held up in most, but not all, cases as the series has progressed. The children from the working classes have by and large remained in those circles, though Tony seems to have become more middle class. Apted has said that one of his regrets is that they did not take into account feminism, and consequently had fewer girls in their study and did not select them on the basis of any possible careers they might choose.

Although it began as a political documentary, the series has become a film of human nature and existentialism. In the director's commentary for 42 Up, Apted comments that he didn't realise the series had changed tone from political to personal until 21 Up, when he showed the film to American friends who encouraged him to submit it (successfully) to American film festivals.