It is widely recognised that language learners require extensive vocabulary knowledge to cope with the demands of studying content fields in English. As well as being rich in general academic and technical terms, academic discourse has been shown to make frequent use of metaphor to express abstract concepts and to achieve rhetorical goals. While research has shown the benefits of raising learners' awareness of the underlying motivation of metaphorical expressions, these findings have yet to be applied to authentic classrooms over longer periods of study. This thesis examines the effects of raising Japanese learners' awareness of metaphorical expressions in a CLIL anthropology course. It examines the written work from two groups of learners: a control group whose language instruction focussed on academic and high frequency vocabulary and an experimental group who received instruction on course-specific metaphorical themes. Variation in metaphor production is compared for the two conditions and across learner abilities, and the interaction between the frequency, dispersion and salience of metaphors in classroom input and learner output is considered. The study then investigates the influences of word frequency, part of speech, phraseology and the L1 on learner metaphor production before concluding with recommendations for pedagogic practice and further study.