As Bloom (1984) stated that the way to increase students' achievements with one-to-one tutorial support can be the subject of instructional technologies today. In this context, the aim of the study was to design, develop and improve a web-based dynamic assessment system aimed at contributing to mathematics learning of secondary school students. For this purpose, a teaching environment has been designed in which 5th grade students can test themselves independently of time and place through internet technologies to learn mathematics lesson topics. A web-based environment combining the principles of dynamic assessment and gamification has been developed with the dynamic assessment algorithm developed within the scope of the research. The research is structured in accordance with the "Type 1" study features, one of the developmental research types. During the development of the prototype, pilot implementation was carried out with 47 5th grade students. In addition, focus group discussions were held with 12 students using the system. According to the findings obtained, it was concluded that the secondary school students' success scores constantly increase in each achievement, the instructional guidance they receive in each test decreases continuously and they can perform the next assessment tasks without help. The students stated that they were directed to the correct solution by the system while solving the questions they did not know, the instructional guidances for the solution were very helpful, the visual elements (monkey, robot and banana) were interesting, fun and beautiful and they wanted to use this system in other lessons.