Early childhood teachers should have extensive knowledge about language and language development, because these facets of professional knowledge are considered as important requirements for fostering language development in early childhood education settings. It is assumed that early childhood teachers acquire this knowledge during pre-service teacher-education, which, in Germany, takes place in different educational tracks (universities and professional schools). With the help of an IRT-based test, the longitudinal change of language knowledge during teacher education at universities and professional schools was investigated in Germany (956 participants at the beginning and 371 participants with non-missing data at both time points). As a result, language knowledge increases during teacher education both at universities and at professional schools. Differences concerning the level of knowledge but not concerning the changes during qualification were found between different educational tracks. Different interpretations are discussed and further research questions are derived.