When is homework beneficial and what makes a homework assignment effective and meaningful? Kohn (2007) offers the following suggestions to principals when working with their teachers on guidelines for assigning meaningful homework:

1. Educate yourself and share what you’ve learned with teachers, parents, and central office administrators.
2. Rethink standardized “homework policies.”
3. Reduce the amount—and don’t stop there.
4. Change the default.
5. Ask the kids.
6. Suggest that teachers assign only what they design.
7. Use homework as an opportunity to involve students in decision-making.
8. Help teachers move away from grading.
9. Experiment.

You can read the explanations for each of these suggestions in Kohn’s article Rethinking Homework.

Research regarding homework has been ongoing for decades. If you look long enough, you can find evidence that supports homework as well as evidence refuting its effectiveness. Marzano and Pickering (2007) developed the following guidelines based on their review of homework research:

• Assign purposeful homework. Legitimate purposes for homework include introducing new content, practicing a skill or process that students can do independently yet with which they need more practice, elaborating on information that has been addressed in class to deepen students’ knowledge, and providing opportunities for students to explore topics of their own interest.
• Design homework to maximize the chances that students will complete it. For example, ensure that homework is at the appropriate level of difficulty. Students should be able to complete homework assignments independently with relatively high success rates, but they should still find the assignments challenging enough to be interesting.
• Involve parents in appropriate ways—for example, as a sounding board to help students summarize what they learned from the homework—without requiring parents to act as teachers or to police students’ homework completion.
• Carefully monitor the amount of homework assigned so that it is appropriate to students' age levels and does not take too much time away from other home activities.

Notice that these guidelines do not suggest whether or not the teacher should actually grade homework. Some research shows that when students are afforded feedback on assigned work, their achievement improves—while other research suggests that not all homework needs to be graded (Marzano & Pickering, 2007).