The main purpose of this research has been to help with the improvement of the quality of schooling as it relates to the number of students in classrooms and its impact on academic achievement. Considering the importance of the quality of education, knowing about the existing conditions and the consequences of increasing/decreasing the number of students per class, could impact policies in regard to the distribution and allotment of educational resources. Current literature on the subject indicate two opinions on the matter: one considers increase in the number of students detrimental to the quality of teaching and learning, while the other regards a slight increase as an agent of improvement through bringing about competition. To clarify this matter a sample of 1294 4th graders of regular public schools in Tehran completed a questionnaire on their school performance/achievement and family conditions. Data analyses indicate that student concentration has no significant effect on grade point average and on math scores. On the other hand, family resources have a significant effect on students’ academic quality. For instance, the presence of father within the home, parental level of education, family income, and having been nursed by mother have a positive impact on the quality of education, while the death of father has a negative impact.