This research adopts the Graduated Prompting Assessment Module of the WATA system (GPAM-WATA) and applies it to the remedial teaching of junior high school mathematics. The theoretical basis of the development of GPAM-WATA is the idea of 'graduated prompt approach' proposed by Campione and Brown (1985; 1987, pp. 92-95). In GPAM-WATA, when examinees fail to answer items correctly, they obtain instructional prompts (IPs) in a graduated way. This research developed the contents of IPs based on the mathematical problem-solving theory of Mayer (1992, pp. 458-460). A quasi-experimental design was adopted. Ninety-six junior high school seventh graders from three different classes participated in this research. The three classes were randomly divided into the GPAM-WATA group (n = 31), the N-WBT group (n = 31) and the PPT group (n = 34). All students received traditional mathematics instruction from the same teacher. After traditional mathematics instruction, all students took the pre-test of the summative assessment. The students in the three different groups then respectively received remedial teaching in the form of GPAM-WATA, normal Web-based test (N-WBT), and paper-and-pencil test (PPT). After the remedial teaching, all students took the post-test of the summative assessment. The results indicate that compared with other groups, performing remedial teaching using GPAM-WATA has significantly better effectiveness. Moreover, it is found that the IPs in GPAM-WATA are effective in remedial teaching for not only those students most lacking in different types of mathematical problem-solving knowledge but also all the other students. (Contains 2 figures and 6 tables.)