Exploring Vocabulary Size and Oral Proficiency in Heritage Brazilian Portuguese

ABSTRACT This study explores language proficiency in heritage language learners of Brazilian Portuguese through the relationship between vocabulary size and oral production. Many studies have assessed the proficiency of those learners by using subjective measures or by using tests that have not been validated experimentally, which is problematic due to the reliability of such measurements. To address this issue, this study used a vocabulary levels test and an adapted version of the Oral Proficiency Interview to estimate vocabulary size and assess oral proficiency. In addition, the study analyzed the metrics of grammatical complexity to compare their contribution to oral performance. Results show that both vocabulary size and grammatical complexity correlate positively with oral performance; however, vocabulary size emerged as the strongest predictor. Furthermore, the study indicates that vocabulary size can be used to differentiate between proficiency levels among heritage language learners.