Internet technology has offered opportunities to develop ongoing assessment systems for classroom-based evaluation--on a daily basis. In this study, the researcher developed a web-based, curriculum-based measurement system with dynamic features which could generate different types of mathematics probes, track students' progress and provide diagnosed information as well as instructional suggestions for teachers. This paper explores the effects of the system on students' mathematical achievements. A total of 134 third-grade students (9- to 10-year-olds) in four classes participated. The teachers in all groups used the web-based curriculum-based measurement system with different types of curriculum-based measurement probes and growth modeling. The results indicated that the use of class-wide dynamic-growth modeling combined with mixed-type probes enabled the students to perform better than those using single-type probes. This outcome was not seen with the linear-growth modeling groups. The positive findings suggested that applying class-wide dynamic-growth modeling as well as the assessment of integrated mathematics competency in the instructional processes facilitated students' mathematics learning. Therefore, the web-based, curriculum-based measurement system was not only an assessment system, but also a tool for teachers to integrate instructional strategies based on curriculum-based measurement.