Background and objectives <p>Although online discussions are widely recognized as an effective instructional strategy in blended learning environments, their differential impacts on learners with varying need for cognition (NFC) remain underexplored. This study specifically examines how online discussion interventions affect learners’ engagement, emotions, and motivation, with particular focus on the moderating role of learners’ NFC.</p> Methods <p>In this study, we conducted a 2 (NFC: higher NFC/lower NFC) × 2 (online discussion intervention: online discussion/non-online discussion) between-subjects design and recruited 95 teacher education undergraduates.</p> Results <p>Results revealed that (a) online discussion intervention led to higher learning engagement, more enjoyment and less boredom than non-online discussion conditions; and (b) learners with higher NFC reported higher learning engagement and autonomous learning motivation, as well as more enjoyment and less boredom than learners with lower NFC. In addition, learners with higher NFC generated more high-quality discussion content than those with lower NFC in online discussions; and (c) NFC moderated the effects of online discussion intervention on cognitive engagement and autonomous learning motivation, with higher-NFC learners benefiting more from online discussions.</p> Originality/value <p>The findings highlight the critical role of bolstering learners’ NFC and demonstrate the necessity of implementing NFC-based dynamic support mechanisms in online discussions. This study provides the first empirical evidence supporting personalized online discussion design based on NFC, contributing to the optimization of pedagogical effectiveness for diverse learner populations.</p>