If you have to provide an incentive, then it's probably not something you should ask of another person. Just be honest. It's a bribe. Or sometimes it's extortion. Either way, is that really the best approach in dealing with people? So next time you are talking with teachers about pay-for-performance, don't say, "money isn't the best incentive." Be honest and say, "I can't be bought off. I teach, because I care about my students."