In this case, I describe a case study I carried out with a class of 5-year-old children. As a primary mathematics teacher-educator, I wished to experience--first hand--teaching mathematics language explicitly, as recommended by many international researchers and also by myself as part of my University courses. The topic taught was subtraction, and the class consisted of 22 children who represented 13 nationalities and 12 languages in all. Following the class teacher's approach, I used English as the medium of instruction, a language that served to "unify" the group and with which the children appeared comfortable. The theoretical framework used to guide the study was the view of learning as participation in a practice, as espoused by Jean Lave and Etienne Wenger, and Götz Krummheuer. In this essay, I outline the teaching experience, explaining the methodological approach, together with practical and pedagogical aspects of the study. [This content is provided in the format of an e-book.]