The present investigation is a cross-sectional quantitative study of the acquisition of Catalan and Spanish past-tense verbs (Preterite, Present Perfect, and Imperfect) by Moroccan children in Catalonia. The data were obtained using elicited story-retell tasks and oral narratives. In both languages, acquiring the correct functional use of verbs is more difficult than making the right lexical or morphological choices. The greatest functional difficulty lies, in both languages, in the acquisition of the Preterite vis-à-vis the Present Perfect. Second in difficulty to the functional dimension is the morphology, where the greatest difficulty in Catalan is in the Present Perfect, whereas in Spanish it is in the Preterite.

These results support a hypothesis that posits that form precedes function. However, they challenge an established position on the acquisition of tense and aspect in Romance languages, which holds that the most difficult functional area for L2 learners of these languages is the difference between perfective and imperfective tenses. The Moroccan children in Catalonia in fact encounter the greatest difficulty in distinguishing between tenses within the perfective area.

Paradigmatic regularity and verb frequency are two linguistic variables constraining the acquisition of function. The regularity and frequency of the verb favor accurate use of the Catalan Preterite and Present Perfect; verb frequency favors accuracy in the Spanish Preterite and Present Perfect.

With regard to the linguistic variables that constrain the acquisition of the morphological dimension, accurate choice of morphology of the Catalan Present Perfect is favored by the transitivity of the verb and the absence of a periphrastic construction, whereas accuracy of morphology of the Spanish Preterite is strongly favored by the absence of adverbs that lead to the Preterite.

Analyses of the socio-demographic variables that constrain the acquisition of verbs reveal that the older the informants are, the better they acquire the functional dimension of the Preterite and the Present Perfect and, most significantly, that the real L2 of Moroccan children in Catalonia is Spanish; Catalan is an L3 learned at a later age and in a different context.