This study investigated the immediate and long-term effects of explicit and implicit classroom interventions on L2 pragmatics. The linguistic focus of the interventions was epistemic stance, which has rarely been studied in research on instructed SLA within the field of interlanguage pragmatics. Eighty-one learners of English at a Japanese university were divided into explicit (n = 37) and implicit (n = 44) groups for 3 hours of instruction. Written production data were collected before the interventions, immediately after them, and five months later. Learners’ use of epistemic stance forms was analysed by using: (i) a measure of individual use of epistemic stance forms; and (ii) learner corpus analysis. The explicit intervention was found to be considerably more effective than the implicit intervention in both the short- and long-term for most of the targeted forms. However, in cases when learners lacked a form for a specific function before the intervention, both types of instruction appeared to be equally effective. While this research generally provides strong support for explicit instruction, the potential of implicit interventions for certain forms needs further investigation.