rabbi says

so i got my rabbi to weigh in on the ol' alfie kohn question. perhaps my summary was not as good as it could be. but r' says that no matter that a child has inherent curiosity. and of course learning should be as intrinsically enjoyable as possible. however. by nature of learning, there is only so much learning that is going to be enjoyable in line with the instinctual enjoyment of the child. at a certain point, there is going to be skill work, or some sort of training that is not going to be enjoyable. the child has absolutely no motivation to do that work. and no incentive to improve his current skill level. without rewards.

(hee hee all these periods reminds me of how the rambam throws in periods).

r' said rewards can be designed so that the students don't do as little as possible to just get the rewards. that is called a badly designed reward system.

r' said it is important to make sure the students do experience the enjoyment of the learning so that the rewards can be phased out. the rewards are to get the student into the pool. the learning must be enjoyable enough to keep them swimming.

if a child has no desire to do it and IF it is something necessary for intellectual development (like working hard at refining the thought process or learning or refining skills or getting to the next level when they are satisfied where they are) then rewards are a training for delaying gratification. until they have the skills to get intrinsic enjoyment.