Mathematics is the basis for further study in a number of school subjects, whereas mathematics problem solving shapes logical reasoning skills that can be applied in many situations in-and-out of school (Dossey, 1992; Ellis, & Berry; 2005). Thus it is not surprising that the rank-ordering of the countries in the mathematics achievement obtained by the large-scale international assessments attracts public attention, yet the results should be observed in the context of differences between national curriculums of the countries involved.

Trends in International Mathematics and Science Study (TIMSS) assess achievement in mathematics and science at the fourth and eighth grades. In respect to mathematics, at each grade, the assessment framework is organized around two dimensions: the content dimension specifying domains to be assessed, and a cognitive dimension specifying the thinking processes. The content domains and the topic areas within the domains are described separately for the fourth and eighth grades, with each topic area elaborated with specific objectives (Mullis, Martin, Ruddock, O’Sullivan, & Preuschoff, 2009).

The TIMSS uses a curriculum model of assessment, in which the curriculum is broadly defined as the major organizing concept in considering how educational opportunities are provided to students, along with the factors that influence how students use these opportunities. The TIMSS curriculum model has three aspects: the intended curriculum, the implemented curriculum, and the achieved curriculum. These embody the mathematics the society intends for students to learn and how the education systems organize themselves to facilitate learning. However this means that what is actually taught in classrooms, teachers’ characteristics, and the very way the content is displayed; may significantly differ between the countries. Especially, to what degree the intended curriculum of a country does cover each test item?

There are three content domains for the TIMSS 2011 fourth grade assessment: numbers, geometric shapes and measures; and data display, while the following cognitive domains describe the sets of behaviours expected of students as they deal with the mathematics content: knowing; applying; and reasoning.

The present study analyses the differential item functioning (DIF) between Finish, Polish. Slovenian, Croatian and Serbian fourth graders in TIMSS 2011 mathematics assessment by using item response models. Slovenia. Poland, Croatia and Serbia are exemplars of post-socialist countries with different trajectories in educational reforms, whereas Finland was used as the reference country. Particular emphasis was given to differences in achievement at each test item and the coverage of national curricula of the five countries that were taken into account. In this vein, we can obtain both strengths and weaknesses of the fourth graders in the five countries in the light of the current curricular content. 

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