To be a good teacher, a teacher must choose the appropriate method. The method helps the educator to manage the lesson plan and learning process as the educator desires. The purpose of the research are: (1) to describe ability of the students who are not taught using Peer Tutoring in learning the functions of six tenses (2) to describe ability of the students who are not taught using Peer Tutoring in learning the functions of six tenses (3) to find out whether there is significant differences between ability of the students who are not taught using Peer Tutoring in learning the functions of six tenses and who are not, and (4) To find whether Peer Tutoring is effective or not in learning the functions of six tenses. In this research, the reseacher used the quasi experimental research design by treatment. In this study, the researcher used the two groups pre-test and post- test where control class was not taught by Peer Tutoring and experimental class was taught by Peer Tutoring. The subjects of the study were the students of Kresna English Language Institute divided into Planet English Program as experimental class and Basic English Program as control class. The number of students in each class is 25 students. To get the data, the researcher used two test, they were pre-test and post- test in both of the groups. The test is about the functions of six tenses. Those are simple present, present continuous, simple past, past continuous, simple future, future continuous. The pre-test was given before Peer Tutoring was applied and the purpose is to describe the level of the students' ability of six tenses before the students are taught by Peer Tutoring and those are not. While post-test was given after treatment, the purpose is to describe the level of the the students' ability of six tenses after the students are taught by Peer Tutoring and those are not. The researcher used SPSS versi 16 to describe the mean, mode, median, etc. Then, it is analyzed by t-test through SPSS, one sample t-test. In control class, score of pre-test is in bad level while the score of post- test is in enough level. It shows that the ability of the students has increased. The t - statistic using r table (5%) is higher than critical value, 2.06. The value is 9.223. In experimental class, the score of pre-test is in enough level while the score of post-test is in very good level. Then, t- statistic (5%) shows that the score is higher than critical value (2.06). It is 38.877. According to t-statistic both of

Key Words: effectiveness, peer tutoring, students' ability of six tenses.