In 2007, the Czech Republic participated in the TIMSS again after eight years (former participation in 1995 and 1999) as the 2003 cycle was missed. Within the fourth cycle in 2007 both grades (4th and 8th) were tested in mathematics and science in the Czech Republic. On one hand, Czech students performed in TIMSS 2007 relatively good in science at both grades. On the other hand, their average achievement in mathematics was found worse - at the fourth grade their average achievement was significantly lower than the TIMSS scale average and at the eighth grade not significantly different to the TIMSS scale average (Mullis et al. 2008; Martin et al. 2008). Trends in average achievement need to be considered very seriously. Although average achievement of Czech students was high at both grades and for both fields in 1995, only Czech students at the eighth grade in science remained high performers in 2007. We already discussed briefly within the TIMSS 2007 national report (Tomášek et al. 2008) that in mathematics the Czech Republic showed a big decline at both grades. In addition, one of the highest declines was found for Czech students in comparison with other European and OECD countries. Thus, the objective of our paper is to analyze possible reasons of such a decline. For the purpose of this paper we focus on mathematics achievement at the eighth grade and our analyses are based on the TIMSS 1995, 1999 and 2007 data files for the Czech Republic. We use regression modelling method and also aim to work with structural modelling approach. Taking into account recent works focused on effects of different educational tracks on differences in achievement (e.g. Horn et al. 2006; Straková et al. 2006) our conceptual framework is oriented more on other aspects, such as school climate, curricular changes. In our paper, we address the following research question ‘To what extent have school climate changes and/or curricular changes effected the decline in math performance of Czech students?’ We expect to identify specific factors that probably caused the negative development in math performance in the Czech Republic.