To assess the relative effectiveness of public and private school environments, researchers must distinguish between the effects of the schools' programs and the students' innate abilities. Student background variables do not appear to account for all the important differences among students attending public and private schools. This document proposes and tests a model of school selection that relates school choice to a family's assessment of public and private school quality. The assumption is that unless private schools appear to offer distinct advantages they would not be selected over tax-supported public schools. The model was tested using data from the High School and Beyond studies of1980 and 1982. The researchers determined that when estimates of the educational production function for public and private schools were corrected for sample selection bias using the school choice model, private schools no longer displayed a significant advantage over public schools in educating the average student. This report describes the model, reviews the data used to test the model, presents the equation that expresses the concepts in the model, discusses the application of educational production functions, and explains how these elements can be manipulated to reveal relative school effectiveness. (PGD)