The present study investigated the development of lexical complexity (LC) in sixth-grade intensive English (IE) students (n = 56) over the course of a five-month program. More specifically, the study analysed oral narratives produced at two points in time (at the beginning and at the end of the intensive period) in order to determine to what extent the program promotes the development of LC. Moreover, the study also compared the progress made by low-level and high-level students to examine whether lexical development differs as a result of differences in initial levels of second-language (L2) proficiency. Findings revealed improvement in LC for all students over the course of the five-month program, but no clear advantage for either of the two proficiency groups.