Private tutoring is a phenomenon that has escaped the attention of researchers, educational planners, and decision makers. Very little is known about its scope, scale, and effects on pupils' achievement and equality of opportunities. Because of its size in a number of countries, and due to it nature--that of a private service oriented at improving academic performance--private tutoring has important implications for the educational system as a whole that cannot be ignored by educational policies. This work contributes to the debate through its systematization of available information and its analysis of this phenomenon. It asks the critical questions: "Who supplies and demands this service?""What effects does it have on the formal education system?" and "What are the policy options facing education planners?" The research draws on existing research conducted in different parts of the world, but primarily in Asia, where private tutoring is particularly widespread. (Contains 83 references.) (DFR)