Ryan and Hemmes (2005) examined how homework assignments are related to learning.The participants were college students enrolled in a class with weekly homework assignments and quizzes. For some weeks, the homework was required and counted toward the student's grade. Other weeks, the homework was optional and did not count toward the student's grade. Predictably, most students completed the required homework assignments and did not do the optional assignments. For each student, the researchers recorded the average quiz grade for weeks with required homework and the average grade for weeks with optional homework to determine whether the grades were significantly higher when homework was required and actually done.