In the last ten years, more and more attention has been paid to the importance of raising the language awareness of language teachers. This is an area in which corpus linguistics has a unique contribution to make. With the help of a concordancer, linguistic features that may be overlooked can be made salient and intertextual information that is implicit in a single text can be made explicit. This paper reports on a study of how corpus evidence was used to address questions sent by English language teachers in Hong Kong to a dedicated website. More than one thousand grammar questions sent to the website over a period of eight years were examined. Three types of most frequently asked questions were identified. The paper discusses how corpus evidence was used to help teachers to notice features and patterns which have escaped their attention and to question long-standing assumptions and misconceptions. It shows how subsequent interrogation of corpus data stimulated by teachers' question often led to new insights into linguistic patterns and language use.