The Economist on Sesame Street: 

Since 1969, “Sesame Street” has been introducing small children to letters and numbers by using clever skits and songs performed by Muppets and celebrities. Patrick Stewart, for instance, reworked Hamlet’s soliloquy as an ode to the letter B (“B or not a B, that is the question”). Now a report by two economists, Melissa Kearney of the University of Maryland and Phillip Levine of Wellesley College, has tracked the first generation of watchers (who were under six in 1969). It reveals that children who had access to “Sesame Street” ended up better prepared for school and were 14% less likely to fall behind in class. 
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The show’s effects are not unlike those of Head Start, a federal scheme that provides poor families with services that include school-based early education. But it costs a fraction as much, says Ms Kearney. “Sesame Street” is not a replacement for early education, which most studies agree is vital; but it is certainly a very affordable supplement. “In essence,” she says, thinking of massive open online courses, “Sesame Street was the first MOOC.”