BSTRACTThis paper reports the results of an investigation into the relationship between school size and achievement. The study examined the impact of school size on mathematics achievement in Dutch, Swedish, and American secondary education and on science achievement in the Netherlands. The following research questions were explored: (1) Is school size related to achievement independently of student background characteristics, such as sex, achievement motivation, socioeconomic status, and cognitive aptitude? (2) Is the effect of school size related to any of the aforementioned background characteristics? (3) Does the effect of school size on achievement differ among the educational systems of the Netherlands, Sweden, and the United States? and (4) Is the effect of school size the same for different measures of student achievement (mathematics versus science)? Datasets from two international studies sponsored by the International Association for the Evaluation of Educational Achievement were analyzed--the Second International Mathematics Study (SIMS) and the Second International Science Study (SISS). The findings found little empiri.al evidence for the existence of school-size effects on achievement in any of the three countries, possibly because school size and curriculum comprehensiveness are not strongly related in these countries. Some useful additional information regarding the robustness of the detected relationships between the five covariates and student achievement is presented. Five tables are included. Contains 39 references. (LMI) *********************************************************************** Reproductions supplied by EDRS are the best that can be made from the original document. *********************************************************************** Netherlands. The analyses sought to provide an answer to the following questions:(1) Is school size related to achievement independently of student background characteristics such as sex, achievement motivation, socio-economic status and cognitive aptitude? (2) Is the effect of school size related to any of the aforementioned background characteristics? (3) Does the effect of school size on achievement differ between the educational systems of the Netherlands, Sweden and the USA? (4) Is the effect of school size the same for different measures of student achievement (mathematics versus science)? It was hypothesized that school size would be most strongly related to achievement in the USA. The analyses, however, revealed little empirical evidence for the existence of school size effects on achievement in any of the three countries, possibly because school size and curriculum comprehensiveness are not strongly related in these countries.Because the investigations involved the analysis of five separate datasets, the research outcomes revealed some useful additional information with respect to the robustness of the detected relationships between the five covariates and student achievement.