We believe that intrinsic motivation is more powerful than extrinsic. Tasks to be evaluated should be meaningful beyond mere instruction or evaluation.
Students have more choices.
A student who really wants to read Hatchet is in a prime spot to learn the concept that fiction is usually placed on the shelf alphabetically by author. The librarian would be using the student's desire for a certain book to teach a specific locational skill. The student researchers will be more intrinsically motivated because they have chosen a topic close to their hearts.