Guided by the mediation approach within sociocultural theory (Thorne & Tasker, 2011), Ma (2017) constructed the sociocultural framework and conducted a study about EFL students’ mobile-assisted language learning (MALL) experience, emphasizing the mediation among mobile technologies, L2 agencies, and other agents. However, the research lacked a focus of a particular skill. In addition, little has been revealed about peer influence that functions as ‘other agents’. The proposed research attempted to address the limitations by focusing particularly on EFL students’ speaking skills with aid of MALL in the format of informal speaking practice among peers. 13 EFL university students in Beijing joined a 6-month experiment and were divided into 2 groups with weekly synchronous and asynchronous practices. The study featured a mixed-methods approach with coding of practices, questionnaires, open-ended feedback, journals, and a semi-structured interview. Findings showed that participants of both modes exhibit more positive views towards their speaking skill development. In addition, they cast light on the effects of peer existence and peer feedback on their speaking performance, as well as their perceived strengths and weaknesses of MALL, reflecting the influence brought by mobile technologies. This research provides inspiration for pedagogies capturing the student-centred speaking practise in the digital era.