Although the debate about school effect has around 5 decades (since Coleman Report, 1966), there remain difficulties in assessing such effect and, above all, in understanding the conditions under which it varies. In other words, we need to deepen our knowledge regarding, for example, the effect of schools social composition, or the effect of pedagogical work of teachers, in the results of students considering their social and national origins. While studies on the school effect have a long tradition in Anglo Saxon countries (e.g. Jencks et al., 1972; Rutter et al., 1979; Smith and Tomlinson, 1989; Entwistle et al., 1997; Thrupp, 1999; Oakes, 2005), other countries only recently have conducted studies on this subject (e.g. Cousin, 1998; Cervini, 2006; Szulkin & Jonsson, 2007; Portela et al, 2007; Pereira, 2010; Seabra et al., 2014).

Specifically, the effects of school composition on student outcomes has been the subject of recent research (Agirdag, Van Houtte & Van Avermaet, 2012; Dumay & Dupriez (2008); Jensen & Rasmussen (2011); Van Houtte & Stevens, 2009) revealing the importance of their role.

Concerning the specific situation of students with immigrant background, the school effect can be different for these students when compared with those who are natives. Generally speaking, we know that students living in disadvantaged social conditions are more sensitive to the effects of the school environment and benefit when they are in more favored environments from a social point of view. But what happens for students who have an immigrant background? Portes and MacLeod (1999) find that in the USA "Mexican-American students do significantly worse than their peers when they are in private schools mostly white, but their scores on the tests are still superior to their co-ethnics in the public schools of minorities"(p.389). On the contrary, "students of Chinese / Korean origin appear as impervious to potential handicaps of the schools they attend: they also have good results in relation to their peers, whether attending high status schools and poor schools with a lot of minority population, [which] once again highlights the vulnerability of children from state of disadvantage "(p.391).

To contribute to this debate, a research was conducted in Portugal, using an extensive data base with the results of fourth and sixth grade students in the Portuguese and Mathematics national exams in Lisbon Metropolitan Area (LMA) in 2009/10. In Portugal about 5% of pupils have a foreigner nationality but in this regional area we can find about 25%. The main objective was to explore the differences in the results of national exams between students with immigrant background and autochthonous, considering the composition of schools. We have analyzed the school composition in three dimensions (social background, ethnic origin and the school performance) and compared these effects in Math’s results and Portuguese’s results.

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