Last night, I was a guest of San Jose State University's economics department on a bus ride through Pebble Beach, complete with drinks and hors d'oeuvres. The reason for the event: the annual Public Choice meetings are being held in Monterey. I live about 10 minutes away.
The conversation jumped from topic to topic, as conversations do, and the issue of externalities from education came up. Also, as happens when that issue comes up, even with free-market-oriented economists, education quickly gets equated with schooling. There's a distinction between the two, as that noted education theorist, Mark Twain, once pointed out.
Then someone said, "As Walter Williams says, there are public externalities up through third grade. By then, kids have learned to read the sign, 'Keep off my lawn.'" (Quote sanitized for public consumption.)