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Almost all (93 percent) parents of children in the experimental group reported that their children subsequently watched the show, compared with roughly one-third of children in the control group (35 percent). Among watchers, those in the experimental group also watched more frequently.

Over six months, from November 1970 to May 1971, the experimental group gained 5.4 I.Q. points — a large effect — relative to the control group and showed stronger evidence of learning along several other dimensions. Gains in cognitive performance were especially large for those who viewed the show frequently relative to those who did so rarely or never. A more recent meta-analysis of published research in 15 countries shows that “Sesame Street” has similar effects around the world.

In newly published research, the economists Melissa Kearney and Phillip Levine examined longer-term effects of “Sesame Street” by comparing the educational outcomes of children and young adults in counties more or less likely to have access to the program during its early years. They found that children living in counties with better “Sesame Street” coverage were less likely to be held behind a grade level.

Other experimental research is consistent with the original “Sesame Street” findings. Low-income prekindergarten children scored higher on a social competence index six months after being randomly assigned to an experimental group, in which their parents were encouraged to replace age-inappropriate television with educational television.

Less reading and more watching

In Norway, and a handful of other developed countries, average I.Q. scores have declined slightly in recent years, after rising for many decades. This is known as the negative Flynn effect, a variation of the more famous Flynn effect, which is named after the psychologist who first published comprehensive evidence of I.Q. gains over time. Among native Norwegian men taking an exam at age 18 for military conscription, those born in 1974 scored two I.Q. points higher than those born in 1987.

In an academic article published this year, the Norwegian economist Oystein Hernaes and his co-authors attributed some of this decline in I.Q. scores to access to cable television, which also coincided with a sharp decline in reading. After the introduction of cable in 1981, Norwegian teenagers and young adults drastically cut back on daily time spent reading from 1980 to 2000, and increased their time watching TV. Moreover, relative to public television, cable television had far less educational content and was focused on entertainment and advertisements.