The ways in which the needs of special populations--students in poverty, English learners, and particularly special education students--have been addressed in studies measuring educational adequacy vary widely. This paper analyzes how these populations have been treated across various adequacy studies, with its major focus on special education adequacy. The study focuses on two primary research questions: (1) What analytical techniques exist for estimating the cost of an adequate education for special education students?; and (2) How might these techniques be applied to estimate the cost of an adequate education for special education students in California, and how do these cost estimates compare to what is currently spent on special education students? Of the four standard adequacy methodologies, only the professional judgment and econometric approaches appear at least theoretically capable of producing comparable stand alone estimates of special education adequacy. Although there are questions as to whether stand-alone special education adequacy estimates can be derived from these types of approaches, to the extent this can be done such estimates would have an important advantage in that the needs of special education students can only be fully considered in relation to the general education services they receive. It is only in this holistic sense that special education adequacy can be fully considered. (Contains 16 tables, 19 exhibits, and 102 footnotes. Appended are the following: (1) Recommended Special Education Staffing Ratios for Wyoming (Based on Parrish et al., 2002); (2) Examples of Panel Configurations of Selected Professional Judgment Panel Studies; (3) Comparison of Base Estimates from Selected Studies Using Both the Professional Judgment and Successful Schools/Districts Approach; and (4) Brief Overview of the Standardized Account Cost Structure (SACS).) [This research was conducted at the request of the Governor's Committee on Educational Excellence, the California Superintendent of Public Instruction Jack O'Connell, and members of the California Legislature. It is part of a larger group of studies coordinated through Stanford University.]