To gain this free bounty, the board didn't actually have to do anything. It needed only to understand something: that the schools were already holding an asset more lucrative than any bake sale. That asset, simply stated, was their students, who by the very nature of compulsory education were a captive audience. If the schools could seize their attention for the purpose of educating them, why not sell off a bit of it for the sake of improving the educational experience?

Tim Wu, The Attention Merchants, loc. 9