Some British researchers have determined that homework is a waste of time.

Homework has always been a waste of time IF it is the type of poorly thought out busy work that many teachers have given their students over the years. Part of the reason for the continuing use of this kind of assignment is nothing but tradition: we’ve always given homework so we must always give it. Part is also the pronouncements of school boards, many of which have set minimum and maximum amounts of homework to be given in some classes and at various grade levels.

There’s nothing wrong with occasionally giving students assignments to be completed outside of class (the British researchers found "homework tended to boost achievement only when done in moderate amounts".). However, to avoid homework being a waste of time, teachers need to make sure the tasks are relevant and enough of a challenge that students will actually need to think rather than simply trade answers with their friends by IM. Like any good assignment, that takes time, work and creativity to write.