Maimonides, a twelfth-century scholar, said, “Twentyfive children may be put in the charge of one teacher. If the number in the class exceeds twenty-five but is not more than forty, he should have an assistant to help with the instruction.

If there are more than forty, two teachers must be appointed.”

Israel follows Maimonides’s rule in determining the number of teachers for each class. How could you use Maimonides’s rule as a natural experiment to study the effect of teacher-student ratios on student achievement?