This study utilised the instant semantic analysis and feedback system (ISAFS) to assist learners in the online discussion learning activities of socio-scientific issues (SSIs) and to document their learning process behaviours for behavioural analyses. The aim was to understand the learners' discussion behaviours during the ISAFS assisted learning process and to guide them in exhibiting more effective discussion behaviours in order to facilitate the learning effectiveness of online asynchronous discussions. The research participants were 55 eleventh-grade students from a senior high school in northeastern Taiwan. A single pre-experimental group design was adopted to collect the learning process data. Eventually, 34 effective samples were considered following the online discussions. The results showed that learners with distinct computer-mediated communication competences and personality traits have different behaviour patterns. Overall, the behavioural analyses reveal that different learning behaviours would result in distinct learning effectiveness, and that learners with different computer-mediated communication competences and personality traits would present various learning behaviours. Based on the research results, suggestions for the application of ISAFS in teaching and implications for future developments are proposed. The findings could be instrumental in the improvement of the teaching process through online discussions.