Historians debate whether the examination system expanded or contracted upward social mobility. On the one hand, the exams were graded without regard to a candidate's social background, and were theoretically open to everyone. In actual practice, the successful candidates had years of a very expensive, sophisticated tutoring of the sort that wealthy gentry families specialized in providing their talented sons. In practice, 90 percent of the population was ineligible due to lack of education, but the upper 10 percent had equal chances for moving to the top. To be successful young men had to have extensive, expensive training in classical Chinese, the use of Mandarin in spoken conversation, calligraphy, and had to master the intricate poetic requirements of the eight-legged essay. Not only did the traditional gentry dominated the system, they also learned that conservatism and resistance to new ideas was the path to success. For centuries critics had pointed out these problems, but the examination system only became more abstract and less relevant to the needs of China. The consensus of scholars is that the eight-legged essay can be blamed as a major cause of "China's cultural stagnation and economic backwardness." However Benjamin Ellman argues there were some positive features, since the essay form was capable of fostering “abstract thinking, persuasiveness, and prosodic form” and that its elaborate structure discouraged a wandering, unfocused narrative”.