The proposed paper details a contrastive interlanguage analysis (i.e. Granger, 1996) of metalinguistic features of certainty and doubt including 'hedges' and 'boosters' (following Hyland, 2000) and 'epistemic stance nouns' (Jiang, 2015) in a 350,000 word corpus of L2 written essays and reports collected at three data points (pre-training, post-training and final assessment) during a 6-credit mandatory freshmen English for academic purposes (EAP) course. The paper explores to what extent freshman undergraduate students are more or less certain in their treatment of theirs' or others' claims via the linguistic devices used prior to their EAP training, and what happens to their use of these linguistic devices as a result of their EAP training. Data was collected from 87 participants spread across five classes with the same participants submitting data at each data point. The results suggest significant impacts of time and task-type on the normalised frequencies and individual wordings of hedging and boosting devices, with pre-training data suggesting significantly more overt hedging and boosting devices used than in the final assessment data and with more epistemic nouns used post-training, and with differences in frequencies and wordings of individual devices across essay and report task types. The longitudinal trend in particular is characterised by a reduction in the use of modals for hedging (‘May’, ‘Would’ etc.) and an increase in lexical means, and a drop in categorical/assumption based statements (‘Undeniably’, ‘Obviously’) to a more academic tone. These findings suggest a positive effect of EAP training on L2 writer’s presentation of their stance on their own or others’ claims, towards the linguistic norms of an academic register.