Using positioning theory as a framework, this study examined two adult learners' participatory opportunities in small group interactions when they were learning English as a second language in an American university. The study finds that control over access to participatory opportunities mainly lies in how learners manage to position themselves and others in group interactions. Respectful and supportive positioning builds up participatory opportunities, whereas exclusive and dominating positioning leads to deprivations. The study discloses that group members' positioning of self and others was largely influenced by the specific context of the interaction dynamics, such as partners' attitudes and responses, characteristics of the task and teacher's intervention, as well as personal attributes. It further suggests that to make group learning more effective, every member needs to construct an agentive position, not only for themselves but also for others, especially for those who might be more vulnerable to being positioned as peripheral in group interactions. In particular, students who are privileged to position themselves as powerful could learn to choose to empower others, i.e. to build up rather than take away opportunities for peripheral students. Findings will contribute to ESL classroom interaction management.