Language play (LP) in second language (L2) classrooms has attracted increasing attention in recent years, but descriptions and explanations of LP construction in English as a foreign language (EFL) settings remain insufficient. This paper reports the discursive processes of LP construction in an elementary school EFL classroom in Korea. I found that teacher/learner agency and the LP production influenced each other bi-directionally in complex ways. Additionally, the LP production was found to relate to teacher authority and inter-student power relations. Interestingly, the moment-to-moment shifts in attitudes on the teacher's and students' parts resulted in the (re)emergence of agency which decided the direction of the practice of LP production, i.e., motivating or demotivating interactants to produce LP. Concerning the students' contextually situated EFL learning outcomes, the ludic function of the LP contributed to an improvement in the outcomes.