The aim of the research aimed at finding out the effectiveness of Climbing Grammar Mountain Game (CGMG) to teach simple present tense, simple past tense and simple future tense. The respondents were 72 students in one of junior high school in Purbalingga in which VIII B as the experimental class and VIII C as the control class. Random sampling technique was used for selecting the sample. In the collecting data, this research used test i.e. pre-test and post-test. The two tests were in the form of multiple choice, gap filling and true false items. This research used t-test as a tool to analyze the data. The result of t-test was higher than t-table. It was 2.379, and the result of t-table at significant level 0.05 for df 70 was 1.667. Then, the calculation of t-obtained with t-table was concluded that t-obtained was higher than t-table (2.379>1.667). In the experimental class, the three different tenses were significant at P<0.05. It meant that the students in the experimental class could understand the grammatical structure of each tense. Finally, Climbing Grammar Mountain Game (CGMG) was effective to teach simple present tense, simple past tense and simple future tense.
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