Many migrants have had few opportunities to develop functional literacy skills, even in their L1. Even so, migration and integration policies in Western host societies often assume literacy skills and fail to consider accommodations for low-literate migrants. Valid, reliable instruments to identify low-literate migrants and policy-oriented research into the assessment of low-literates are scarce. This study makes a contribution to research and practice in this area. It reports on the development of a valid multilingual assessment tool to efficiently shed light on adult migrants' literacy skills. This tool was trialed on a representative sample of 351 asylum seekers in Belgian asylum centers. The performance data were analyzed using Rasch Measurement, and DIF analysis. First, the results confirmed the tool allowed for the identification of four literacy levels. Second, frequency distribution of the Rasch person measurements showed that a substantial proportion of asylum seekers do not possess the literacy skills to participate fully in their host society upon arrival. The findings underline the importance of (a) taking literacy skills into account in both integration policy and assessment; (b) viewing literacy as a broad functional spectrum while considering the influence of contextual factors such as language of assessment and processing time.