The general aim of this longitudinal study was to look at literacy acquisition of multilingual good and poor spellers (hereafter GS and PS) in German and French with a special emphasis on spelling. For this purpose GS and PS were selected in grade 2 in German and followed up to grade 4. The focus was on this period as in Luxembourg literacy is acquired through German from the first grade and written French from grade 3 on. The interval between grades 2 and 4 thus represents a critical period for written second language acquisition. The native language of the children, Germanic (e.g. Luxembourgish) or Romanophone (e.g. Portuguese), adds another linguistic characteristic. Research focused at the development of biliteracy but some multilingual aspects were analyzed. Abstract The first two studies differentiate between top-level processes related to semantics (e.g. vocabulary) and bottom level processes implied in literacy (e.g. spelling). The first two studies established that the native language has an impact on reading comprehension as Germanic speaking children have an advantage on German tasks and Romanophone children an advantage on French tasks. By contrast, performances on bottom-level processes such as spelling and reading are not influenced by the native language. Structural equation models revealed that German top-level processes did not influence French top-level processes. Concerning bottom-level processes however, there was an influence from one academic year on the following as well as from German on French. Abstract The last three studies focused on differences between biliterate GS and PS in German and in French. The third study examined the reading and spelling strategies (e.g. the application of orthographic rules) that both groups of children acquired in German and in French. Although GS outperformed PS, their overall reading and spelling performance patterns were different in German than in French. GS applied orthographic rules more systematically than PS in German. In French, both groups were ...