This paper provides evidence from a study of ESL speakers that cross-language transfereffects interact, sometimes in very subtle ways, with developmental effects in the construction ofL2 syllable structures. It extends Broselow and Finer's (1991) proposal for the MinimalSonority Distance Parameter-Setting (MSD) model in L2 syllables by (a) adding evidence from alanguage that unambiguously exhibits transfer in complex onsets and (b) examining syllablecodas to see whether the MSD parameter can be extended to account for the distribution of errorpatterns there, as well. The results of the study generally support the predictions that the MSDmodel makes for consonant cluster difficulty in specific syllable positions; however, it does notmake predictions about the patterns that are found in learner error types. We argue thatoptimality theory (Prince & Smolensky, 1993) provides a more explicit account of theinteractions between transfer and developmental effects in L2 syllables, allowing us to interpretwithin a singular grammatical framework not only why learners have difficulty withspecific ESL structures but also how they resolve it.