The best way that I've found to increase student buy-in for an activity, project, or assessment, is to offer choices. When testing with an essay, provide several topics and allow students to choose which one they'll answer. For a project, list a variety of options that include interesting tasks to the students. This method encourages them to take control of their learning and again, reinforces the teacher's role as facilitator.
Teaching Tip: The Power of Choice
PreK–K, 1–2, 3–5