This study explored teachers' perceptions of synchronous online peer interaction (SOPI) among young learners (YLs), aged 7 to 15. Thirty-eight teachers of diverse L1 backgrounds and teaching experience completed a survey and attended an in-depth interview that explored multiple aspects of SOPI (e.g. benefits, issues, frequency of use, strategies to promote SOPI's effectiveness, and mediating factors). Survey data were analysed using exploratory factor analyses to identify themes/constructs related to areas of SOPI under investigation, and inferential statistics were reported to examine teachers' self-ratings of different aspects of SOPI. Interviews were analysed following a content-based approach to supplement the quantitative data. The results show that teachers believed SOPI promoted YLs' attention to language aspects and created a peer-support learning environment. SOPI's effectiveness was affected by multiple factors (e.g. learners' individual differences, teachers' guidance, grouping, and learners' financial and family backgrounds). Teachers expressed the importance of using SOPI for YLs in online classes and suggested instruction/guidance to maximize its' benefits. However, the frequency of use of SOPI was reported to be dependent on schools' regulations and resources, learners' affective aspects, and parental support. The results also indicate the impact of teachers' online teaching experience on their differential perceptions of online SOPI.