The relationship between school achievement and social class has been a central concern in international educational research in recent years. Findings of comparative studies in educational achievement such as PIRLS or TIMSS (Bos 2007; Bonsen 2008) have consistently shown that students from socially disadvantaged backgrounds are less successful in school than their socio-economic more privileged classmates. In sociological perspectives it is argued that the genesis of educational inequality by social class should be understood as an unequal distribution of cultural and economic resources. With Boudon (1974) the creation of social inequality within educational contexts unfolds into primary effects (socially determined academic performance) and secondary effects (socially determined educational choices). However, previous research still fails to explain which impact school education and in detail school exercises may have in creating social class differences in school performance.
The current study examines how social inequality is reproduced on the level of school classroom and aims to explain, to what extend working with ‘realistically contextualized’ and ‘pure mathematical’ items can lead to discriminating children with lower socio-economic status (SES). To investigate this we combine sociological perspectives with didactics of mathematics. 
From a sociological point of view findings will be interpreted with Basil Bernstein´s code theory (Bernstein 2005). His theory offers 1) possibilities to describe characteristics of test items via classification and framing and 2) ways to describe requirements of test items from a learner’s perspective via recognition and realization rules 3) explanations for social differences in performance with different types of mathematic items. Mathematical educational circles e.g. mathematic curricula emphasize contextualization of mathematics is both, motivating for students and useful for everyday life. Considering what is sociologically known about socio-cultural orientation of meanings, speech forms and modes of responses (Holland 1981), the present project examines, whether there are unintended negative consequences for students from social disadvantaged backgrounds when working with items that embed a mathematical problem in a realistic setting.
In England Cooper and Dunne (1998/2000) already identified that, lower SES students, compared with higher SES students, perform less well on ‘realistic contextualized’ items in comparison with ‘pure mathematic’ items. In addition qualitative analyses have shown that lower SES children are more likely to draw inappropriate on their everyday knowledge than higher SES students and that these effects can lead to an underestimation of student´s actual existing mathematical knowledge.
In reference to the theoretical and empirical framework that has been stressed out, two central research questions are to be investigated by the current study: On the one hand students from lower SES background are expected to do considerably less well on items which have been classified as ‘realistic’ than students from higher SES background. On the other hand none of these socio-economic effects are expected to be found in case of ‘pure mathematical’ items. Both research hypotheses are supposed to show, that not IQ but socio-economic background factors are responsible for these phenomena.

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