During the last decade, most research studies have analysed online synchronous interactions in written mode (textchat), highlighting the benefits of chatting for the development of learners’ oral proficiency. The environment used in our experiment is multimodal and based on a synchronous audio conference. Analyzing interactions in such an environment is rather new in Computer Assisted Language Learning (CALL). This study is related to false-beginners in an English for Specific Purposes (ESP) course, presenting a high degree of heterogeneity in their proficiency levels. We use two approaches. One is quantitative and involves learners’ participation in audio and textchat. The other is qualitative and relates to the complexity of professional discourse. Firstly, we provide a method that accurately measures oral participation in the two modes. Then, within this framework, we report that heterogeneous linguistic levels do not constrain learners’ oral participation, outlining the equalizing role played in this instance by the textchat. Moreover, this type of environment supports oral production by false-beginners who have over a period of years become unaccustomed to learning and speaking in a foreign language, and leads them to regain self-confidence. The qualitative part of our study shows that false-beginners can cope with professional conversations at different levels of complexity.