Seth Godin on captive and not-so-captive audiences
Marketer, author and speaker Seth Godin has written about his time with 75 eighth graders (S1 kids) and how some of them just weren't wanting to engage with him. He's right when he says that they miss out on something by not listening in to what he's saying, but he's wrong in apportioning the responsibility to engage on them.
As a teacher who's had more than his fare share of kids who start off not wanting to engage - with anything, let alone me or my subject - I had to find ways to get them engaged so that they did get something good out of their time.
So while Seth found himself giving more to those who were engaging with him I don't think it's right to expect an audience to engage with you "just because". You've got to give them a reason to engage and that means understanding each and every one of them quickly. How do you do this? Engage quickly with those who are not engaged and find new ways to get everyone on board. If you want to find out how, go and take a look in a classroom near you ;-)