Vocabulary development is essential for learning, but conventional vocabulary assessments lack the range and flexibility to support K-12 classroom teachers in making instructional decisions. Drawing on linguistics, educational psychology, and educational measurement, this book offers a fresh perspective on word learning and describes powerful, precise assessment strategies. Guidelines are presented for selecting which words to teach, evaluating the depth and richness of students' word knowledge and their ability to apply it in complex contexts, designing effective instructional practices, and using technology to create adaptive and scalable assessments. User-friendly features include sample test items, classroom examples, a glossary, and suggested print and online resources.