This study examined the effects of low-achieving children's use of helping tools in a synchronous mathematics peer-tutoring system on the children's mathematics learning and their learning behaviours. In a remedial class, 16 third-grade students in a remedial class engaged in peer tutoring in a face-to-face synchronous online environment during a 7-week period. In comparison to their 18 counterparts in the control group, the students in the experimental group had a very significant gain in the mathematics learning. The helping tools, especially the indicating errors function requested by the tutee to the tutor, had significant effects on learning achievement for low-achieving children. The tools also facilitated the tutor's demonstration of solutions, indicating errors and the provision of guided instruction. Several patterns of peer-tutoring behaviour in face-to-face online peer-tutoring sessions were identified. The findings support the effectiveness of the helping tools in enhancing children's tutoring behaviours in a face-to-face online peer-tutoring environment.