Findings presented herein are a part of a large international study of primary school final grade student achievement in mathematics and science (TIMSS 2003). Studies were also conducted on the degree of correlation between student family socioeconomic status, mathematical self-concept and achievement in mathematics. Pilot studies, whose findings are discussed comprised 112 seventh-grade students. "Family socioeconomic status" was defined by variables such as the number of family members, economically disadvantaged/affluent home, and parental educational status. "Mathematical self-concept" was defined as one of the more narrow domains of academic self-concept. "Achievement in mathematics" was measured by the test assessing two dimensions of knowledge of mathematics: content and cognitive skills. The analyses of partial correlations indicate that the most significant predictors of achievement in mathematics test are as follows mathematical self-concept, mother’s educational status and some indicators of family socioeconomic status (access to the Internet, number of household members, number of books available at home). Concerning the correlation found between family characteristics and mathematical self-concept and achievement in mathematics, the developers of current changes in mathematics teaching should not disregard the findings of this study.