Read the article by Joshua D. Angrist and Victor Lavy, "Using Maimonides' Rule to Estimate the Effect of Class Size on Scholastic Achievement," in The Quarterly Journal of Economics 114, no. 2 (1999): 533-575. Explain why Maimonides' rule is a good instrumental variable for class size. Without such an instrumental variable, if we regress pupil performance on class size with ordinary least squares, give one reason why the effect of class size may be underestimated and one reason why it may be overestimated. Can you think of another good instrumental variable for class size? Explain.