In this paper, the authors draw on Alexiadou and Anagnostopoulou's (1998) proposal concerning [+/-null argument] languages as well as on the works by Zobl and Liceras (1994), and Vainikka and Young-Scholten (1998) concerning the role of free and bound morphology in L1 acquisition in order to investigate two different agreement morphological paradigms (those of Spanish and English) in two bilingual children. More specifically, the authors analyze, within the same 'population', three different types of verbal agreement spell-outs (free [+pronominal] agreement morphemes, like nominative pronouns in English; bound [+pronominal] agreement morphemes, like Spanish person agreement markers in V; and bound [-pronominal] agreement morphemes, like English third person singular marker -s) and, based on the different acquisition patterns displayed by these elements, argue that: (i) the bound/free morphology dichotomy is too general to account for the patterns of L1 acquisition of so-called weak and strong morphological paradigms (Speas 1994; Alexiadou and Anagnostopoulou 1998) which differentiate English and Spanish; (ii) while a radical separation between bound and free morphology is too restricted in that it obscures the fact that strong and free morphemes share abstract features, the distinction has been legitimized by the syntactic differences between the two languages (Alexiadou and Anagnostopoulou 1998); and (iii) taking into account both productivity and error index, grammatical and ungrammatical occurrences point towards a hierarchy of agreement spell-outs in which Spanish emerges as the less problematic language.