In this article the results of an explorative study of the Dutch language proficiency of advanced second-language learners are presented. The proficiency in Dutch of a group of 17 students from non-indigeneous linguistic minority groups was compared with the Dutch proficiency of 17 native age-mates. In each group, 16 of the 17 students went to a 'MAV0', an intermediate level of secondary education. Their Dutch language skills were measured by analyzing spontaneous language samples and by administering some tests. In general, the second-language learners (the A-group) were shown to have a lower Dutch language proficiency than the native students (the N-group), and especially with respect to their scores on the tests. It was tentatively concluded that the students from the Α-group had a Dutch language deficiency in the area of Cognitive Academic Language Proficiency. Their Basic Interpersonal Communicative Skills (the concepts CALP and BICS are borrowed from Cummins' theoretical framework) were more or less similar to the skills of native Dutch students. Students from linguistic minority groups might succeed in higher levels of secondary education if their CALP were brought to a higher level, since CALP correlates strongly with the kind of language proficiency demanded in school.