This article examines how learners of English as a foreign language process reduced relative clauses (RRCs) from the perspective of usage-based language learning, which posits that language knowledge forms a hierarchy from item-based knowledge consisting only of entrenched frequent exemplars to more advanced schematized knowledge. Twenty-eight Japanese undergraduates provided phrase-by-phrase reading times for frequent and infrequent RRC exemplars. Immediately after the experiment, the participants also made stimulated-recall comments on their thought processes employed during sentence processing. Both the reading-time data and the stimulated-recall data show that the learners who comprehended infrequent exemplars as well as frequent exemplars had computed syntactic relationships at the key regions of the sentences in real time, and that those who could not comprehend infrequent exemplars had not. These results suggest that the former type of learners successfully activated the RRC schema while the latter learners failed to do so.