If any one fact has emerged consistently in the International Project for the Evaluation of Educational Achievement (IEA) studies of educational achievements, it is that achievement is related to a variety of factors in the home background of children. This is true so far as differences in the achievements of single students within a country are concerned. It is also true so far as mean score for different countries is concerned. Several questions can be posed with respect to these relationships. Firstly, how substantial are the relationships, both within and between countries? Are they merely "statistically significant," or are they of a size that has "practical significance?" Secondly, how stable are the relationships from subject matter to subject matter and from country to country? Are the factors that receive most weight as predictors of reading the same as the ones that receive most weight for prediction of science or of literature? Are the factors that are most predictive in the U.S.A. also most predictive in England or Iran or Chile? If not, what reasonable explanation can be offered for the differences? Thirdly, are the facts that are most predictive of individual differences also the ones that are most predictive of national differences? If not, why not? In spite of the modest correlations that we obtained for background variables, these seemed to be much more effective predictors than any of the items that described the school as an educational unit. [Reproduced from the best available copy.] (Author/JM)