Speaking is a challenge for most English learners owing to the lack of practicing environments and partners. The virtual reality (VR) technology has changed this situation by providing learners with rich opportunities for practice. In VR-based practicing environments, peer tutoring is a common strategy for promoting peer assistance. However, in conventional VR-based learning, students may merely follow the guidelines and content provided by the teacher without thinking about the meaning and reasons for the practice in the situated contexts, which generally leads to poor learning outcomes. To solve this problem, a progressive question prompt-based peer-tutoring approach in VR contexts (PQP-PTVR) is proposed to assist students' English-speaking development. An experiment was conducted to evaluate the effectiveness of the proposed approach. The experimental group used the proposed approach, while the control group learned with the conventional question prompt-based peer-tutoring approach in VR contexts (C-PTVR). The results showed that the experimental group achieved significantly greater improvement in speaking and self-efficacy than the control group. Concerning the participants' learning behaviors, the experimental group had more interactions and made more attempts to improve their speaking. This study contributes to the existing literature by proposing the PQP-PTVR approach to enhancing learners' speaking development, improving their interactions and self-efficacy.