Problem Statement: Models of academic vocabulary use need to address discursive and functional linguistics perspectives in order to enhance construct validity and authenticity in academic vocabulary assessment, particularly with regard to the testing of word families.Purpose of Study: To provide a clearer picture of academic vocabulary use that can inform the design of academic vocabulary testing by enhancing construct validity and authenticity.Method: A survey of the literature on academic vocabulary has been conducted to present various perspectives and their shortcoming. Then, findings from the functional linguistics and discourse analysis traditions with regard to vocabulary use are discussed. An example of a testing item incorporating functional perspectives on the use of derivatives within a lemma is presented.Conclusion: Incorporating functional and discursive findings related to the discourse-structuring functions of multiple derivatives of a single lemma may lead to more valid and authentic academic vocabulary tests and teaching practices.