Which brings us to that second number of the day: 15. That, shockingly, is where Nielsen says Sesame Street ranks among the top children’s shows on the air. Some months, it does even worse. Ask a preschooler who her favourite TV character is, and chances are she’ll say Dora, Curious George or, heaven help us, SpongeBob. The Children’s Television Workshop (now called Sesame Workshop) produces only 26 episodes a year now, down from a high of 130. The workshop itself recently announced it was laying off 20 per cent of its staff as the recession continues to take a toll on nonprofit arts organisations. But Sesame Street is no ordinary nonprofit. It is, arguably, the most important children’s programme in the history of television. No show has affected the way we think about education, parenting, childhood development and cultural diversity. You might even say that Sesame Street changed the world, one letter at a time.

When Sesame Street arrived, scientists were just discovering that our brains were not fully formed at birth and could be affected by early experiences. Head Start began in 1965, in part, out of that revelation. “Educators were virtually ignoring the intellect of preschool children,” says Joan Ganz Cooney, who threw that dinner party and has been the show’s visionary since the beginning. Children would eat up the ABCs before kindergarten, Cooney believed, especially if a wacky puppet ate up alphabet-shaped cookies along with them. The Department of Education was sceptical. But the government agreed to contribute half of the original $8 million budget to launch Sesame Street.

The results were pretty immediate. The first season in 1969 set out to teach children to count from one to 10, but it became clear that kids as young as 2 could make it to 20. (The show now hits 100, counting by tens.) That rookie year also yielded three Emmys, a Peabody Award, a front-page rave from The New York Times and one especially noteworthy piece of fan mail from Richard Nixon.

The most impressive feedback, however, came from the kids themselves—or at least from their test scores. No show to this day has probed its effects on kids as thoroughly as Sesame Street, which plans to spend more than $770,000 in 2009 on its department of education and research. When people think of Sesame Street as the essence of educational television, what they don’t realise is how much the show has educated the educators. Independent research found that children who regularly watch Sesame Street gained more than nonviewers on tests of letter and number recognition, vocabulary and early math skills.

But the show was never just about improving test scores. Perhaps the most radical part of the Sesame DNA has always been its social activism. From the start, Sesame targeted lower-income, urban kids—the ones who lived on streets with garbage cans sitting in front of their rowhouse apartments. The show arrived on the heels of riots in Washington, Baltimore, Cleveland and Chicago, and the assassination of Martin Luther King Jr. “It was intentional from the beginning to show different races living together,” says David Kleeman, executive director of the American Center for Children and Media.

Sesame Street is now exported to 16 countries and regions. In South Africa, where as recently as 2008 the president insisted that HIV does not cause AIDS, the show features a ginger-coloured, HIV-positive Muppet. In 1998, a Middle East version was launched, coproduced by Israelis and Palestinians. The Israeli and Palestinian Muppets lived on different streets, but they would sometimes visit each other to play. Israeli Muppets could appear in Palestinian territory, but not without being invited. But the intifada made the notion of coexistence and cooperation politically untenable and it was cancelled. The show returned in 2006, but now there are separate versions produced for Israel and the Palestinian territories. The Palestinian one no longer features Jews at all.

Guernsey is the author of Into the Minds of Babes: How Screen Time Affects Children From Birth to Age 5