The present study investigates the role of L1 transfer in the L2 acquisition of Spanish inchoative structures with se (La ventana se rompió 'The window broke') by adult L1 English speakers at different levels of proficiency. Different verb classes were tested, and main comparisons were established between alternating unaccusatives (romper 'to break') and non-alternating transitive verbs (cortar 'to cut'). Group and qualitative analyses of the data were conducted. Evidence in favor of the view of L1 transfer as a developmentally moderated process was found. The data did not support full transfer in early acquisition nor a modular view of transfer.