The aim of this study was to identify the effect of using the eclectic model on the achievement of the eighth grade students of mathematics and their motivation to learn. To verify this, a teacher's manual was prepared in the functions and equations unit according to the selective model. The researcher also prepared an achievement test in the functions and equations, and its validity and stability was measured on asurvey sample The study sample consisted of (58) students from the eighth grade students in Muscat Governorate. They were divided into two groups: an experimental group that studied the unit of functions and equations using the selective model and a control group that studied the same unit in the usual way. The study found the following results: • There was a statistically significant difference at the level of significance (a < 0.05) between the mean scores of the experimental group and the scores of the control group students in the achievement test in favor of the average scores of the experimental group. • There was no statistically significant difference at the (a < 0.05) level between the mean scores of the experimental group and the average scores of the control group students in the motivation scale for mathematics education. In light of these results, the researcher recommended that teachers, and curriculum development should be informed of the eclectic model in order to increase students 'academic achievement in mathematics, she also recommended to encourge teachers to carry out studies of programs to improve students' motivation to learn mathematics.