There is an increased focus on educational quality and learning outcomes in Sweden, especially since international comparative studies like TIMSS has put the limelight on declining study results in core subject like mathematics. School-effectiveness is therefore an urgent issue. The aim of this study is to identify factors that contribute to the explanation why some schools is effective but others are less effective in terms of the students’ academic achievement in mathematics on TIMSS. This is conducted by examining Sweden in contrast with school-effectiveness in some high achieving countries in Europe and Asia-Pacific. The framework of multilevel analysis was used, since it is important to separate the effect of school-level variables from the effect of home environment and to take care of the sampling design used in TIMSS 2007. The results show that different educational system identifies different school level factors when controlling for home background. Noteworthy is that very few school level factors were significant in the full models. The single most important factor for school- effectiveness appears to be student behavior in school. Offering enrichment or remedial in mathematic seem to have different effects in different countries. Professional development opportunities for the teachers and the use of different incentives do not seem to have any effect in any of the countries, except in Chinese-Taipei. Disappointingly, we were unable to detect any significant school level factors in Sweden. A possible reason for this is that we excluded variables that have been altered in any of the countries, since we do believe that such changes might be a threat to the validity. Hence, it is possible that important questions in the Swedish context were excluded.