For one thing, all of us act based on our own perceptions of the world, not on the perceptions of others. Adults often refuse to follow the advice of doctors to lose weight if they are not convinced losing weight is as important as the doctor thinks it is. Simply telling students they have to do homework because it's important is never going to be effective if we can't convincingly counter their complaints that it's not. For another, the reasons teachers give for assigning homework often match up badly with the specific assignments they make, another case of "talking the talk" without "walking the walk." For example, assigning homework to increase student mastery of the subject isn't going to work if the assignments are simply repetitions of skills a student has already mastered.

Moreover, reasons that go beyond academic achievement, such as teaching students to work without supervision, are suspect in any event. In an exhaustive review of research on homework, Harris Cooper found that "no study has examined whether noninstructional purposes (e.g., creating parent awareness, punishment) have their intended effects" and concludes that "most problematic [in the research on homework] is the number Of homework outcomes that remain unresearched . Implied questions about policy are important ones: Who decides what kind of out-of-school student habits and child-parent interaction should be promoted? And why should the school be doing such promotion? And how do we know that homework is a good tool for noninstructional goals, anyway?