Choosing relevant vocabulary to teach in ESL composition courses can be a difficult task for instructors. They often rely on intuition rather than empirical methods for vocabulary selection. This paper presents two case studies where corpora were used either to select vocabulary items for instruction or to scaffold student learning of vocabulary through exposure to corpora. Corpora and language analysis tools were used to complement vocabulary selection and instruction. This vocabulary selection process complements perceptual approaches as it provides empirical measures for the selection and a data driven approach to learning as instructors teach and students learn contextually relevant words.