The aim of this study is to find out the effect of using Klausmeier's Model and the Approaches to Studying on students to acquire the mathematical concepts. The sample of the study consists of (152) students from the ninth grade distributed into six educational classes : four classes at Monir bin AlNayer school of basic education (5-12) and two classes at El-Heda school of basic education (3-12). It is assured that these classes are equal in levels before performing this experiment.. To collect data , the researcher designed Achievement Test to measure the extent of which students acquire mathematical concepts . The test was checked for validity and reliability. The researcher also used the Revised Approaches to study Inventory (RASI) to classify students to three groups: deep approach , strategy approach and surface approach groups. This tool has been translated and validated to suit Omani environment. After collecting and analyzing the study achieved the following results : There are statistical differences at the level " a = 0.01 " between the average marks of the students in the ninth grade in the achievement test concerning acquire mathematical concepts and this is due to the teaching method and for Klausmeier's Model . There are statistical differences at the level " a = 0.01 " between the . average marks of the students in the ninth grade in the achievement test concerning acquire mathematical concepts due to the Approaches to study and for the strategy approach , then the surface approach ,finally the deep approach. According to the results the researcher recommends' to apply these models in teaching the educational curricula and this to raise the students educational standards and the study, also refers to the importance of the students approach's towards the study and the necessity of performing more studies in this field.