This study aimed at investigating the impact of a Cooperative Learning Model on self-motivation and academic performance in high levels of learning in students. The method of the study was quasi-experimental and the educational action was performed in two experimental groups; Hamyar Dabir cooperative teaching was employed in one group and in the other group, the same method together with students’ selfassessment for eight 90-minutes sessions were employed. The population consisted of all male students in third grade of high school in Birjand city and the sample consisted of 54 individuals in the form of three groups each consisting of 18 individuals (two experimental groups and one control group). The sample was selected using purposive sampling and the study tools consisted of a part of Motivated Strategies for Learning Questionnaire (MSLQ) by Pintrich and De Groot (1990) and a researcher-made geometry academic progress test for measuring low and high levels of cognitive domain. One-way analysis of variance and Tukey test were used for investigating the self-motivation test data. For analyzing the data from academic achievement test mixed analysis of variance was used. The main findings of the study indicate that “cooperative learning and self-assessment” are effective in improving “self-motivation” of students in geometry course. Also, “cooperative learning and self-assessment” had significant impact on and created difference in components of self-motivation or “motivational beliefs” in the groups. In addition, Hamyar Dabir (cooperator with teacher) cooperative learning model and self-assessment had positive impact on both high and low levels of learning of students in the cognitive domain.