The purpose of this study is to demonstrate that dynamic assessment based instruction increases children's learning by using a quasi-experimental research design in Korea. In this study, dynamic assessment is defined as a measurement method of the zone of proximal development (ZPD) as well as the qualitative and quantitative diagnostic information for individual children. In addition, dynamic assessment based instruction is defined as a teaching method using the diagnostic information types in order to increase children's learning. In this study, 59 children between the ages of 4 and 5 participated. Three types of number concept achievement tests (pre-test, parallel test, and post-test) for each age group were developed and the content validity, face validity, and split-half reliability were examined. After conducting the pre-test, the children of each age group were divided into an experimental group and a control group. Dynamic assessment based instruction regarding number concepts was undertaken only with the experimental group for 4 weeks. Both groups took a post-test after completing the 4 weeks of classes. The ANCOVA technique was used for data analysis. The result of this study shows that dynamic assessment based instruction has a significant effect on children's learning of number concepts (in the case of 4-year-old children, F = 12.34, p less than 0.01; 5-year-old children, F = 20.03, p less than 0.01). Therefore, dynamic assessment based instruction should be used widely for children's cognitive learning. (Contains 4 figures and 13 tables.)