This is one of nine volumes describing the results of extensive research carried out by the International Association for the Evaluation of Educational Achievement (IEA) over a seven-year period. The overall aim of this extensive empirical study is to relate student competence to instructional, economic, and social factors which account for differences between students, schools, and national systems of education. In this volume, the rationale behind the model used in the analysis of data collected in the IEA Six Subject Survey is provided. A model of causation is advanced to relate the various input measures to achievement in the six subject areas of Science, Reading Comprehension, Literature, English and French as Foreign Languages and Civic Education. The compounding of variables and their organization into blocks are discussed. The order in which these blocks are introduced to the analysis reflects the belief that earlier events in the life of the individual student have influenced later events in the student's life and schooling. Details of the sampling techniques used in the survey as well as the limits of confidence which can be placed on the statistics are described. The development of the attitudinal scales used is outlined in an Appendix. (Author/BJG)