Hands-on concordancing is often described as the future of computer assisted language learning, but first there are two problems. Its benefits have been hard to validate empirically, and it is conceived for advanced learners while the majority receiving formal language instruction are intermediate. This study describes the adaptation of concordance technology to lexical expansion, the development of a suitable interface (a concordance-based lexical tutor), and its testing with intermediate university students in Oman. The tutor exposes learners to 2400 words over two terms, the basic high-frequency words of English. The learners are lexicographers using the concordance to make a dictionary, deciding which words to include (metacognition) and searching for clear example sentences (multicontextual exposure and negotiated input). Results from use of the tutor are strong. Used as directed it replicates features of incidental learning from natural exposure but in a much compressed time frame.