Marginal Analysis of Senior-itis

We have all probably heard of "senior-itis", the phenomenon of High School or College Seniors losing interest in the outcome of their classes. It's likely that the phenomenon is largely caused by simple boredom, but marginal analysis seems to shed some light on this phenomenon. Early in a scholastic career, each grade affects GPA greatly. With the completion of each class, however, the effect of each grade on GPA decreases. This will continue to the point that in the senior year, GPA may not even budge in response to one's grades. In economic language this is a decrease in the marginal benefit of getting a higher grade in a class. Thus the return from an investment in studying time decreases, and students may find it reasonable to decrease their studying to a new equilibrium. Obviously, students will not want to incur the cost of repeating a class due to failing, and this is a separate issue. Thus the new equilibrium will always be above a failing grade, no matter how small the marginal change to GPA will be, but it will decrease to lower levels as more courses are completed. This little bit of economic analysis may partially explain why bored high school and college seniors might aim for C's in their classes.