Andrew Leigh

Oscar the Grouch gives children permission to feel sad. Big Bird questions everything. Mr. Snuffleupagus is the imaginary friend. Count von Count loves mathematics. Grover embodies self-confidence. Ernie delights in practical jokes. Bert has an utterly different personality to Ernie, but is his best friend nonetheless. Zoe proves that girls can be both dainty and strong. Kermit the Frog is always a gentleman.

Nov. 10 marks the 50th anniversary of the moment when “Sesame Street” first aired on television. But it’s not just a day for nostalgia; it’s also a time when we should recall what a remarkable venture the show is, and the extent to which it is grounded in careful science and hard data.

In 1967, when Joan Cooney began to plan “Sesame Street,” she envisaged a collaboration between creative designers and experts in child development. At a time when children were watching “Looney Tunes” and “The Flintstones,” this would be a television program that followed its own academic curriculum. Most unusually, the Children’s Television Workshop would use evidence to shape the show.

In its first year, “Sesame Street” was evaluated in a randomized trial. Much like the way we assess new drugs, this compared a treatment group (children who were encouraged to watch the program) with a regular control group. Unfortunately, the researchers hadn’t reckoned on the show’s popularity. With more than one-third of American children tuning in to each episode, there wasn’t much difference in viewing rates between the two groups.

So the next year, researchers took a different approach — focusing on cities where “Sesame Street” was only available on cable and then randomly providing cable television to a subset of low-income households, whose children were encouraged to watch Big Bird and friends. This time, there was a big difference in viewing rates between the control group (without “Sesame Street”) and the treatment group — and a significant difference in vocabulary. Children who watched “Sesame Street” had the same cognitive skills as non-viewers who were a year older.

In the past half-century, over 1,000 research studies have been conducted on “Sesame Street," and many of them have fed back into the show’s development. In one experiment, the show’s designers wanted to find out how best to teach preschoolers the functions of their eyes, nose and mouth. Groups of young children were randomly assigned to watch either a test video featuring Grover interacting with a little girl named Chelsea, or a video with Elmo pointing out body parts on the “Mona Lisa.”

When tested afterwards, children who had been allocated to watch the video with Grover had a better grasp of how their body parts worked than children who watched the video with Elmo. The researchers concluded that the painting was too abstract a teaching tool, and that children learnt body parts best in a segment featuring both a Muppet and a human actor.

Another question was how many letters of the alphabet should be taught in each episode. “Sesame Street” designers randomly assigned preschoolers to watch episodes with two “Letters of the Day” or with one “Letter of the Day.” They found that doubling up on the letters wasn’t an effective way to teach. Asked afterwards to correctly identify letters, children who watched episodes with two letters were less likely to know either of them than children who had watched an episode with just one letter.

Research even determined which subjects went to air. A pilot program about the death of storekeeper Mr. Hooper showed that it gave children a better understanding of death, without adverse reactions. But a pilot about the divorce of Mr. Snuffleupagus’ parents left some children in the test audience with the mistaken impression that all parental arguments invariably lead to divorce. “Sesame Street” aired the show about death, but the program about divorce was never broadcast.

The pioneers who developed “Sesame Street" were, and still are, brilliant and unorthodox. But perhaps the greatest secret of the show’s success has been the willingness of its creators to rigorously put their theories to the test.