The prime purpose of the current study was to investigate the effect of the predictive power of Jigsaw strategy on low proficient students' proficiency in mathematics and determine the effect of Jigsaw strategy on the mathematics achievement of middle-grades grade-two students. The current study included 80 students who were enrolled in the mathematics lessons in 2017-2018 academic year. Of the total sample, forty were included in an experimental group and forty were in control group. The experimental group was given Jigsaw strategy intervention whereas the control group was taught following existing traditional method (teacher-centred). The findings of the study showed that Jigsaw strategy had more positive effect on students' overall mathematics achievement than the control group students. Additionally, the findings also revealed that experimental group students also exhibited positive attitude towards the mathematics lessons. These overall findings have some implications on learning and teaching of mathematics in Iraq context. This study also provides ample evidences that teacher-centered method is obsolete and ineffective especially in teaching mathematics.