This paper reports on a test of the validity of Pienemann's (1998) Processability Theory (PT). This theory predicts that certain morphological and syntactic phenomena are acquired in a fixed sequence. Three phenomena were chosen for this study: attributive adjective morphology, predicative adjective morphology, and subordinate clause syntax (placement of negation). These phenomena are located at successive developmental stages in the hierarchy predicted by PT. We test whether they actually do appear in this predicted hierarchical order in the L2 of Danish, Norwegian, and Swedish learners. The three languages mentioned are very closely related and have the same adjective morphology and subordinate clause syntax. We can, therefore, treat them as one language for the purposes of this study. Three analyses have been carried out: The first follows Pienemann's theory and is concerned only with syntactic levels; the second is a semantic analysis of the acquisition of number versus that of gender; the third analysis studies the various kinds of mismatches between the inflection of the noun, the controller, and the adjective. The results are the following: The first test supports PT as it has been described by Pienemann. The second analysis shows that there is an acquisitional hierarchy such that number is acquired before gender (in adjectives), and the mismatch analysis raises questions about the fundamental assumptions of the theory.