We exploit supply-driven heterogeneity in the expansion of cable television across Norwegian municipalities to identify developmental effects of commercial television exposure during childhood. We find that higher exposure to commercial television reduces cognitive ability and high school graduation rates for boys. The effects appear to be driven by consumption of light television entertainment crowding out more cognitively stimulating activities. Point estimates suggest that the effects are most negative for boys from more educated families. We find no effect on high school completion for girls, pointing to the growth of noneducational media as a factor in the widening educational gender gap.