The work is based on PISA 2009 International Assessment Study. Two counties were selected: a developed country, Estonia and a developing country, Azerbaijan. The following Datum was used for statistical analysis: students average scores in reading (162 schools, 4 600 students from Azerbaijan; 17 schools, 4 923 students from Estonia). The work is based on mixed type research. The main goal is to determine the effect of different independent variables related to school, student, and household, on students' achievements in reading in developed and developing countries. Three research questions were developed: (1) To what extent are student background variables associated with reading scores in each country?; (2) To what extent are family-related variables associated with reading scores in each country?; and (3) To what extent are school-related variables associated with reading scores in each country (variables were analyzed separately: organizational; instructional; and teacher-related)? As with other research studies this research may have some limitations regarding research model, data analyses, and interpretations. For data analyses t-test and General Linear Model--Univariate statistics were applied. General Findings: Estonia: Most of the teachers apply modern teaching methods; students' attitude towards reading activities, teacher, and school are positive. Parental involvement has a positive effect on students' achievements in reading. Azerbaijan: The majority of the teachers do not apply modern teaching methods; students' attitudes towards reading activities are not deemed positive; students have negative attitudes towards school and teachers. The research showed that different factors work differently in developed and developing countries cases.