644 adolescents. On average, ethnic minority students report higher levels of externalising problem behaviour than Dutch majority students, but this difference decreases with increasing numbers of other minority students in class. When minority students constitute about two-third of the class, their level of problem behaviour equals that of the Dutch majority group. For Dutch students, no effect is found of the proportion of minority students in class. With respect to internalising problem behaviour, no ethnic den- sity effects were found. The proportion of minority stu- dents in class is not related to the level of internalising problem behaviour of either ethnic minority or Dutch majority students. Furthermore, both groups do not differ with respect to their average level of internalising problem behaviour. It is important to notice that these effects were found while controlling for a large number of individual level variables. In line with former studies, we found that girls are more inclined to reveal internalising problems, while boys are at higher risk for reporting externalising problems. In- ternalising problems, but in particular externalising prob- lems tend to grow with age. Pupils in the lower educational strata furthermore are more inclined to report both inter- nalising and externalising problems. Likewise, the level of family afﬂuence has a strong effect on internalising prob- lems, adolescents from more afﬂuent families reporting less internalising problems. In addition to these well-known effects, ethnic minority students report higher levels of externalising problems but only when they belong to school-classes where Dutch autochthonous students are in the majority. Thus, the increased risk attributed to a non- Western ethnic background appears to be a explained by minority status more than by the ethnic background as such. It should be noted that whereas we ﬁnd our hypothesis on the ethnic density effect conﬁrmed for externalising problem behaviour, no effect of the proportion of minority students in class on internalising problem behaviour has been found. This result can be considered rather surprising. It suggests that externalising problem behaviour may be more susceptible to social inﬂuences and change according to differences in the social context. The conclusion might be that among migrant youth, externalising problem behaviour, such as aggressive behaviour, is evoked only in situations where they are also in a minority position and not or less so in a social context that is characterised by cultural diversity. This can be considered in line with the results of the study by Monshouwer et al. [16], who observed that a culturally diverse school composition with a majority of ethnic minority students tends to lower alcohol consumption of students, but only in those with a minority background. Hence, they concluded that, within a school-context, peer modelling and reinforcement mecha- nisms can affect individual students’ alcohol use. 123 Soc Psychiat Epidemiol (2010) 45:639–646 Aggressive and delinquent behaviour as well appear to be susceptible to social norms and peer inﬂuence. With respect to anxiety, depression, and somatic complaints, norms and peer pressure are less likely to have such an impact. In addition, the fact that the density effect was controlled for individual background characteristics may explain its insigniﬁcance for internalising problems. Hen- derson et al. [12] found a signiﬁcant ethnic density effect on depressive symptoms (internalising) in a population sample, but once individual socioeconomic characteristics were taken into account, the signiﬁcance of neighbourhood characteristics or ethnic density effects disappeared. Strengths and limitations In our study, the density effect is operationalised in terms of minority status rather than ethnicity. Students in our sample come from different ethnic backgrounds, a con- siderable part of them belonging to four of the major ethnic minority groups in the Netherlands (i.e. Turks, Moroccans, Surinamese and Antilleans), but also a relatively large group coming from a large variety of other non-Western countries. However, we cannot assume that relations between different groups are always good, namely, inter- ethnic tensions between minority groups may exist and may complicate the interpretation of our ﬁndings. On the other hand, all these minorities share the common char- acteristic that they do not belong to the ethnic Dutch majority and are culturally different from this group. Being ‘allochthonous’ (the Dutch term for being of non-Dutch and non-Western origins) often means sharing a relatively marginalised position in Dutch society, revealed by rela- tively low educational accomplishment and relatively high unemployment rates for migrant youth in the Netherlands [27]. Similarity in this respect may outweigh the match in speciﬁc ethnic background, as other authors have also argued [20]. It is possible to argue that only the presence of members of one’s own ethnic group may result in more intimate or supportive relations and can increase feelings of acceptance, but it seems equally likely that the presence of other minority students that are not necessarily of the same ethnic group may increase tolerance and acceptance of diversity in general, and of minority students in particular for all students in class. Regarding the measurement of ethnicity, there are some limitations to the way in which minority status was ascri- bed in this research. We used the ofﬁcial Dutch deﬁnition for non-Western immigrants [27], which includes both ﬁrst and second-generation immigrants from non-Western countries. Although at this point the third generation in general has not yet reached high school age, future studies could include self-reported ethnicity in addition to using the country of birth of the respondent and his or her parents