The aim of the research is to find out the effect of applying classroom assessment techniques (CATs) on both mathematical and logical thinking among fourth-grade scientific students. In pursuit of the research objectives, the experimental method was used, and the quasi-experimental design was used for two equivalent groups, one control group taught in the traditional way and the other experimental taught according to the techniques of classroom structural evaluation. The research sample consisted of (44) students from the fourth scientific grade who were intentionally chosen after ensuring their equivalence in several factors, most notably chronologi-cal age and the level of mathematics, and they were distributed equally among the two groups. To implement the research, three tools were built, represented in the teacher's handbook for applying the class formative assessment, the mathematical reasoning test, and the logical thinking test. The two researchers applied the exper-iment in the first semester of the academic year (2019/2020) AD. The two re-searchers applied the techniques of class formative assessment to the experimental group, while the control group studied according to the usual method, and then the mathematical thinking test and the dimensional logical thinking test were applied. On the experimental and control groups. The results showed that there were statis-tically significant differences between the mean scores of the two groups on the mathematical thinking test, and there were also statistically significant differences between the mean scores of the two groups on the logical reasoning test. The size of the effect of applying the class formative assessment on both thinking was calcu-lated, and it appeared that it had a clear effect on both mathematical thinking and logical thinking. In light of the results, the two researchers recommended a number of recommendations.