Through the lens of a community of practice as a social learning system, this article analyses the peer interactions of a group of four college learners of English as a foreign language in a peer feedback activity with the focus on the writer -- the top student, Wang. The study uses an ethnographical way to interpret Wang's discourse actions in participation in a learning group of four as part of the English-classroom community of practice. The focus of the analyses is on the practices for understanding how Wang constructed her identities as a way of participation; how she, as well as the other learners, identified with the practices; how the peer feedback activity as a social learning system worked; and what Wang learned from it. The study witnesses three modes of Wang's identification with this local English-learning community of practice (engagement, imagination and alignment); her changing participation in terms of modulating her identity investment in the social practice (as a master, novice and non-participant); the different meanings negotiated or circulated in the learning system (linguistic, social, interpersonal, etc.); and the implicit as well as explicit knowledge Wang may learn from it.