The theory of Organic Grammar is applied to four decades of work on children’s and immigrant L2 learners’ acquisition of German word order and inflectional morphology. New data from a longitudinal study of ab initio secondary school students reveals bottom-up acquisition of syntactic structure during their exchange year in Germany. Their naturalistic acquisition process, with stages described for the first time in L2 acquisition, is highly similar to that of younger learners. This has important implications for German teaching and for Universal Grammar and acquisition.