We use heterogeneity in the timing of television's introduction to di¤erent local markets to identify the e¤ect of preschool television exposure on standardized test scores during adolescence. Our preferred point estimate indicates that an additional year of preschool television exposure raises average adolescent test scores by about .02 standard deviations. We are able to reject negative e¤ects larger than about .03 standard deviations per year of television exposure. For reading and general knowledge scores, the positive e¤ects we …nd are marginally statistically signi…cant, and these e¤ects are largest for children from households where English is not the primary language, for children whose mothers have less than a high school education, and for non-white children.
JEL classi…cation: I21, J13, J24Keywords: television, cognitive ability, mediaWe are grateful to Dominic Brewer, John Collins, Ronald Ehrenberg, Eric Hanushek, and Mary Morris (at ICPSR) for assistance with Coleman study data, and to Christopher Berry for supplying data on school quality. Lisa Furchtgott, Jennifer Paniza, and Mike Sinkinson provided outstanding research assistance. We thank Marianne Bertrand, Stefano DellaVigna, Ed Glaeser, Austan Goolsbee, Jim Heckman, Caroline Hoxby, Larry Katz, Steve Levitt, Ethan Lieber, Jens Ludwig, Kevin M. Murphy, Emily Oster, Matthew Rabin, Andrei Shleifer, Chad Syverson, Bob Topel, workshop participants at the University of Chicago, Harvard University, UC Berkeley, the NBER, the University of Notre Dame, and the APPAM, and four anonymous referees for helpful comments. E-mail: gentzkow@ChicagoGSB.edu, jmshapir@uchicago.edu.
I IntroductionTelevision has attracted young viewers since broadcasting began in the 1940s. Concerns about its e¤ects on the cognitive development of young children emerged almost immediately, and have been fueled by academic research showing a negative association between early-childhood television viewing and later academic achievement. 1 These …ndings have contributed to a belief among the vast majority of pediatricians that television has "negative e¤ects on brain development" of In this paper, we identify the e¤ect of preschool exposure to television on adolescent cognitive skills by exploiting variation in the timing of television's introduction to U.S. cities. 2 Most cities …rst received television between the early 1940s and the mid-1950s. The exact timing was a¤ected by a number of exogenous events, most notably a four-year freeze on licensing prompted by problems with the allocation of broadcast spectrum across cities. Once it was introduced, television was adopted rapidly by families with children. Survey evidence suggests that young children who had television in their homes during this period watched as much as three and a half hours per day, and contemporary time-use studies show reductions in a wide range of alternative activities, including sleep, homework, and outdoor play. Evidence on television ownership suggests that the di¤usion 2 of television was broad-bas...