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