Foreign-Heid is often associated with weaker school performance. They make a division between the home language of the student and the school language. It is often assumed that the home language would be the acquisition of the school language in the way. But in Flanders, there is little research on the effects of non-native performance and the current investigation is limited to the Dutch division versus foreign language students. However, this division is not realistic. In reality, of a foreign language are presented more as a continuum of all Dutch to completely different language. The MARS project, the way the home language is narrow therefore measured. The measuring instruments used in the Validiv project (http://www.validiv.be/)om examine the home language of pupils are subjected to a thorough psychometric analysis to ensure the reliability and validity. Furthermore, the usefulness of these instruments is checked. In addition, also observed class groups, teachers were interviewed and focus groups with students organized to examine the multilingual reality. This research is done in both primary and secondary schools. Results are expected in the summer of 2015.