The Informative Boundary Hypothesis (IBH: [4]) claims that a prosodic boundary is interpreted relative to preceding boundaries. This study tests predictions of the IBH with Korean learners of English (L2ers) and English native speakers (L1ers) in a prosody experiment on the resolution of an Early vs. Late Closure ambiguity in spoken English sentences. A control experiment assessed and controlled for English morpho-syntactic knowledge in the main experiment. The main experiment presented the syntactically ambiguous portion of sentences in a forced-choice continuation-selection task. The results showed that 1) Korean L2ers at all levels used relative boundary size to disambiguate sentences, like L1ers; 2) intonation phrase boundaries provided stronger evidence for syntactic boundaries than intermediate phrase boundaries, especially for the L2ers; and 3) the IBH's 3-way categorization of relative boundary size - larger/same-size/smaller - appears insufficient for this syntactic structure.