This study aimed to investigate the factors affecting the performance of eighth-grade students in mathematics at the International Study (TIMSS) from the perspective of teachers, supervisors and students regarding the following domains: the textbook, the teacher, the student, and the material and human potentials. The population of this study consisted of all students in the eighth grade participating in the International Study (TIMSS, 2011) with a total of (3478), and their math teachers (368), and the supervisors (74) in each of the educational governorates (Muscat, Batinah North, Batinah South, and Dakhiliya).The sample of the study consisted of (351) male and female students, and (126) teachers and supervisors from the four governorates. The researcher developed two questionnaires, one for the students and a different one for both teachers and supervisors. The questionnaire consists of 65 items. The validity of the iestionnaires was carried out through a panel of (24) judges and the reliability was calculated by Cronbach - Alpha coefficient which was found to be (0.83) for the students questionnaire and (0.88) for the teachers and supervisors questionnaire. The results of the study revealed that the factors affecting the performance of eighth grade students in mathematics at the International Study (TIMSS) from teachers and supervisors' point of view are: student, material and human potentials, teacher, the textbook respectively. As from the perspective of the students the factors are: physical and human potential, textbook, teacher, and student respectively. The study found statistically significant differences on the teachers and supervisors perspectives on these factors, which are in favor of males in the domain of textbook. As for the occupation variable, it was in favor of the supervisor in the teacher domain. The results of the students' questionnaire revealed significant differences in favor of male in the students' domain. The results of the study showed no statistically significant differences in the variable of experience of teachers and supervisors. According to the results of the study, the researcher recommended the following: continuous and effective communication between mathematics teachers and those in charge of the development of mathematics curricula, and to accustom and train students to solve questions similar to the questions of TIMSS test. The researcher suggested further research to be conducted on this topic. For example, conducting a comparison of the results of the International Study (TIMSS) between countries of, and low achievement, like the Sultanate of Oman in the characteristics associated with the following variables: the student, the teacher, the curriculum, and the school