This study investigated how peer comments made using a video annotation tool (VAT) through an online learning community improved student-teachers’ level of reflective thinking and communication competence throughout the simulated (i.e., role-play) context of consultation practice. Eighty student-teachers from two classes of the course “Comprehensive School Guidance” participated in this study, and all recorded two videos for their tripartite practice on parent consultation for self-evaluation and peer comment. Forty student-teachers were in the comparison class and provided general comments to their peers on the learning platform, while those in the experimental class used the VAT on the learning platform to provide specific comments to their peers. Two post-practice online questionnaires and reflective journal entries, which aimed to measure communication competence and reflective thinking ability, were administered to the student-teachers after the first and second consultation practice. The reflective journal entries were segmented into units of analysis that were scored using a 4-level model of reflective thinking (from 1 to 4), with a higher score indicating demonstration of a higher level of reflective thinking for that particular segment. Both the number of reflective notes made and the average level of reflective thinking in student-teachers’ journal entries were indicators of reflective thinking ability. Two mixed ANOVAs were conducted to examine whether student-teachers in the experimental (VAT) class improved their reflective thinking ability and communication competence more significantly than those in the comparison (non-VAT) class. The results showed that student-teachers in both the VAT and non-VAT classes had statistically higher scores for communication competence and reflective thinking in the second role-play practice. Student-teachers with the support of VAT, in comparison to those without, significantly improved their average reflective thinking ability. Focus group interviews were also conducted to investigate how VAT could support student-teachers’ learning process and to learn their perceptions of the strengths and limitations of the VAT. The results indicated that the VAT could enhance student-teachers’ learning by reducing communication barriers created by the tendency to avoid direct observations of peers’ weaknesses, enhancing reflection-in-action during practice, and contextualizing written comments by referring to specific video segments. However, student-teachers felt that the VAT should also allow users to draw on the video screens.