Abstract
This study investigates changes in productive vocabulary knowledge among pre-intermediate L1 Japanese learners of English using the Self-Reflection Writing Task (SRWT). Unlike established tasks such as the Lexical Frequency Profile (LFP; Laufer & Nation, 1995), Productive Vocabulary Levels Test (Laufer & Nation, 1999; PVLT), and Lex30 (Meara & Fitzpatrick, 2000), the SRWT requires learners to write a brief reflective text on a familiar topic related directly to their learning experiences. The study included 24 L1 Japanese learners of English enrolled in a compulsory English Communication Skills class. Participants completed the SRWT by reflecting on their final presentation performance, writing between 130-160 words. The task was repeated at the end of each study quarter (Q1, Q2, and Q3). Responses were analyzed using the new JACET8000 corpus (JACET, 2016), categorizing vocabulary as either frequent (1k) or infrequent (non-1k). The findings suggest a possible two-phase pattern in learners’ productive vocabulary development. Initially, learners appear to rely primarily on frequent (1k) vocabulary, establishing a foundational lexical base. As their vocabulary knowledge develops, they gradually begin incorporating more infrequent (non-1k) lexical items in their writing. This shift may indicate a deeper stage of vocabulary development in which learners move beyond basic lexical resources to express ideas more precisely. These findings highlight the importance of strengthening frequent vocabulary knowledge in language instruction while gradually supporting learners’ expansion toward less frequent vocabulary.