This paper examines private tutoring systems in three East Asian countries (Japan, South Korea, and Cambodia) with the purpose of examining the relationship between those systems and formal education systems. The study of private tutoring systems in each nation can be used to reveal the inadequacies of the formal education system in meeting the ideal of equal opportunity of education in relation to high-stakes examinations. In each nation, the private tutoring system functions as a "shadow education market" to absorb unmet demand for additional education in a parasitic relationship with the formal system. Governments have enacted various policies to respond to the growing private tutoring systems which have proven largely ineffective and often led to further expansion. Pedagogical and curricular practices in the private tutoring systems have functioned to increase "anxiety" and "insecurity" in regard to the formal education system with the purpose of expanding the market. Studies of mass schooling systems and equal opportunity are incomplete without due consideration toward the role of the private tutoring system. Efforts toward education policy-making and reform to further the ideal of equal opportunity of education must be informed by such research on private tutoring. (Contains 6 tables.)