The study investigated how student tutors of Big Buddies Club, a community service tutoring English to elementary school students, learned and used classroom language in the prep training and tutoring program. The subjects of this qualitative study were four students tutoring a group of class 3 and 4 tutees. The data were collected through observation and documents. The results show that in prep training, student tutors learned classroom language through lecturing, saying classroom language and getting feedback when mispronunciations occurred, teaching practice, and sharing ideas with fellow tutors. In teaching practice, student tutors employed three out of eight types of classroom language. However, they lacked the opportunity to analyze their performance. In tutoring activities, student tutors used five types of classroom language. They employed some strategies to make the classroom language comprehensible for the tutees: repeating, translating into Indonesian, using 'wait time', providing modeling, gestures, and actions, and mixing the expressions and instructions in English and Indonesian. After eight meetings, they gained better fluency and pronunciation. As the community service has provided opportunities for students to learn and practice English, the program contributes a new insight of EFL pedagogy in Indonesia.