Derivational knowledge, the ability to understand and produce derivatives of a word, is essential for vocabulary learners to expand their lexical knowledge. Earlier research (e.g., Schmitt & Zimmerman, 2002) has shown that L2 learners may have limited ability to produce derivatives compared to L1 speakers. However, the degree to which productive derivational knowledge differs between L1 and L2 learners, and among learners at different levels of vocabulary knowledge has yet to be examined. The present study investigated the extent to which L1 English speakers (n = 23) and L2 English learners (n = 107) at varying vocabulary levels (1000‐5000) could produce the derivatives of 90 headwords in a decontextualized derivative recall test. A generalized linear mixed model indicated that L1 and L2 productive derivational knowledge significantly differed, and L2 productive derivational knowledge differed among learners with different vocabulary levels. However, the results revealed that the L1 speakers and the learners who had mastered the higher vocabulary levels (3000–5000) produced a similar number of derivatives in the decontextualized recall test. The findings suggest that learners’ vocabulary levels could be indicative of L2 productive derivational knowledge to some degree. Lastly, the results are discussed to provide pedagogical implications for teaching and assessing L2 productive derivational knowledge.

Research has indicated that first language (L1) English speakers acquire derivational knowledge-the ability to understand and produce derived forms of a word-through increased exposure to the language (e.g., Anglin, 1993). Second language (L2) research has shown that L2 English learners tend to have limited productive derivational knowledge in comparison to L1 speakers (Schmitt & Zimmerman, 2002). However, the degree to which productive knowledge of derivatives differs between L1 speakers and L2 learners remains unclear. Moreover, there have yet to be any studies that have compared productive derivational knowledge of L2 learners at different educational levels (undergraduate and graduate students), nor has research examined L1 and L2 production of derivatives according to the frequency levels of the target items. The present study compared the ability of 21 L1 speakers, 18 English as a second language (ESL)-speaking graduate students, and 61 English as a foreign language (EFL) undergraduate students to produce the derivatives of 30 headwords.The results indicated that L1 speakers produced significantly more derivatives than ESL graduate students and EFL undergraduate students, and ESL graduate students outperformed EFL undergraduate students.

This study explores the effects of receptive derivational affix knowledge, derivative frequency, part of speech, and vocabulary breadth on production of derivatives. Twenty-one speakers of English as a first language and 107 learners of English as a second language were asked to produce derivatives for 90 prompt words on a decontextualized derivative form-recall test. Results indicated that (a) increased receptive derivational affix knowledge and derivative frequency were linked to greater accuracy in production of derivatives, (b) adverb derivatives were more frequently produced compared to other parts of speech, and (c) learners' vocabulary breadth was associated with greater accuracy in producing derivatives. Results also indicated a larger facilitative effect of derivative frequency for second language learners in comparison to first language speakers, but this effect diminished as vocabulary breadth increased. These findings suggest that learners may initially acquire derivatives on a case-by-case basis but, as their knowledge of derivational affixes and vocabulary breadth increases, they may acquire derivatives more systematically.

Acquiring vocabulary knowledge is a vital part of L2 learning because vocabulary plays a significant role in every mode of communication (reading, listening, writing, and speaking). For learners to become independent users of a L2, they must know many thousands of words and learn how to use them well in communication. For example, learners of English must acquire up to 9,000 words (e.g., happy) and their morphologically-related forms (e.g., happiness, unhappy, happily) to comprehend spoken and written texts (e.g., conversation, television programs, films, novels, and newspapers) (Nation, 2006; Webb & Rodgers, 2009a, 2009b). Moreover, acquisition of L2 vocabulary entails learning different aspects of word knowledge such as word parts, collocations, and associations, not only learning form-meaning connections. Thus, the teaching, learning, and researching of L2 vocabulary can be highly complex. The purpose of this chapter is to provide a guide to researching instructed second language vocabulary acquisition. The chapter sets out to provide (1) an overview of key concepts in vocabulary research, (2) a brief overview of L2 vocabulary research focusing on intervention studies, (3) an overview of a frequently employed study design (pretest-posttest design), different measures for assessing L2 vocabulary knowledge as well as options and cautions for interpreting data, (4) advice for future vocabulary researchers, and (5) tips to overcome potential challenges.