This study examined the impact of a second language (L2) on how event phases are categorized. The aim was to test how strong a boost the L2 system provides when learners are trained to classify events in a new way. The targeted linguistic contrast was the grammatical expression of change-of-state events in progress, available in English but far less so in Chinese. Advanced Chinese learners of English received categorization training in four conditions: action-biased, completion-biased, verbally-distracted, and with overt L2 encoding. Experiment 1 tested the extent to which learners' first language facilitates event categorization. Experiment 2 compared learning success in L2-based categorization with and without verbal interference. Experiment 3 measured the benefits of explicit L2 verbalization for L2-based category learning. The results showed that L2 grammar has a graded impact on learning, categorization with overt verbalization having the highest, followed by categorization in silence, and categorization with verbal interference the lowest, although not significantly reduced.