The present paper reports on a study that investigated the role of procedural and declarative memory in the acquisition of Finnish past tense morphology. Two competing models were tested. Ullman's (2004) declarative/procedural model predicts that procedural memory supports the acquisition of regular morphology, whereas declarative memory supports the acquisition of irregular morphology. In contrast, single-route approaches predict that declarative memory should support lexical learning, which in turn should predict morphological acquisition. One-hundred and twenty-four (N=124) monolingual Finnish-speaking children aged 4;0–6;7 completed tests of procedural and declarative memory, tests of vocabulary knowledge and nonverbal ability, and a test of past test knowledge. The results best supported the single-route approach, suggesting that this account best extends to languages that possess greater morphological complexity than English.