Throughout an educational career, literacy skills become more elaborated. However, little is known about the development of reading and writing skills in foreign languages in adolescents. In this contribution, we focused on the development of language skills in the foreign languages English and French in Germany as measured by a C-Test. Hereby, we aimed to explore the potential of C-tests to provide a differentiated approach to the assessment of foreign language development in secondary school students. We draw on the data from the German panel study "Multilingual Development: a Longitudinal Perspective" (MEZ) on students' language skills in the foreign languages English (n = 1987) and French (n = 662). We investigated the differences in the means of "classical" and "word recognition" scores in English and French C-tests and the development of these differences. The application of both scores in our study provided differentiated information on students' receptive and productive aspects of literacy in adolescents and showed that students in secondary school are still on their way of developing spelling skills in both foreign languages. Furthermore, our results reveal that the receptive and productive components of language proficiency show different developmental patterns at various stages of foreign language learning.