The main objective of the study is to identify the changes in the Russian contextual characteristics from 2001 to 2006 that contributed to the progress of student achievements in PIRLS. Basic research questions are: 1) how can we explain the significant positive growth in students' achievements? and 2) are there groups of students who did not show the identical improvements and how can we distinguish between these groups? Methods of regression analysis, cluster analysis and analysis of variance have been used. The study discovered the factors which were significantly connected with positive dynamic of students' attainments. In particular, an increase in the percentage of students from families with high levels of reading activities has significantly contributed to the positive growth of students' reading attainments from PIRLS-2001 to PIRLS-2006. Also the study helped to identify groups of students that did not improve their achievements. For example the schools with high percentage of primary grade students coming from economically disadvantaged homes did not show significant differences in average achievements. Comparative analysis shows that some significant factors in Russia are different from factors in other countries that made progress from 2001 to 2006.  E.g. both factor 'Students' reading aloud in class' and factor 'Teacher's highest level of formal education' are significant for Russian good achievements but not for some other countries that made progress from 2001 to 2006 such as Hong Kong, Singapore and Italy.