This research aims to know the effectiveness of teaching with a proposed strategy according to the common Knowledge construction modelin mathematical proficiency among students of the second middle class. The researchers adopted the method of the experimental approach, as the experimental design was used for two independent and equal groups with a post-test. The experiment was applied to a sample consisting of (83) students divided into two groups: an experimental comprising (42) students and a control group, the second comprising (41) students., from Badr Shaker Al-Sayyab Intermediate School for Boys, for the first semester of the academic year (2021-2022), the two groups were rewarded in four variables: (chronological age calculated in months, previous achievement in mathematics, intelligence test, and information test in mathematical proficiency).The two research tools represented in the mathematical competency test with its cognitive domain and the product tendency scale that represents its emotional domain were built,Their validity was verified, and the reliability coefficient was calculated for them, and it was acceptable. The coefficients of difficulty, discrimination, and the effectiveness of wrong alternatives for the objective paragraphs of the mathematical proficiency test were also found, and all of them were also acceptable. One of the researchers taught the students of the research sample represented by the experimental and control groups during the period of the experiment, which started on Wednesday (10/11/2021) and ended on Monday (17/1/2022), and after the experiment ended, the two research tools were applied to the students of the research sample.. To treat the information statistically, the researchers used: (t-test, Pearson correlation coefficient, alpha-Cronbach equation, difficulty coefficient equation, discrimination power coefficient equation, efficacy equation of wrong alternatives, Cooper equation, and Eta square equation). After analyzing the data, the results showed that there was a statistically significant difference in favor of the experimental group, as the value of the effect size was equal to (0.127), which is an average effect size that indicates the effectiveness of the proposed strategy.