Abstract The present study aims to verify previous findings on the role of proficiency in the degree of complexity and accuracy of verbal morphemes in written essays from intermediate and advanced L2 Italian learners. In addition, by taking the perspective of usage-based theories on the distributional properties in the input, it investigates the extent to which contingency affects morphological complexity and accuracy by the emergence of cue-outcome associations. Hypotheses on the effects of contingency and proficiency on complexity and accuracy, and on their mutual relationships, are verified by adopting a confirmatory approach and by using Structural equation modeling. Results support the claims for non-universal mechanisms in the acquisition of verbal morphology: proficiency does not affect the morphological complexity of learner texts in the same way in inflectionally rich and poor languages, and the cue-outcome mechanisms of associative learning work to different extents depending on the inflectional systems of the target languages.