A typical Mathematics class is comprised of a heterogeneous group of students in terms of academic ability, learning styles, intelligence quotient, home background and the likes. The inability of the teachers to effectively manage these differences usually leads to poor academic achievement among the learners, especially the weak ones. This study therefore determined the effectiveness of Cooperative Learning Technique on low learning ability students in Mathematics. Quasi-experimental research design was adopted. The sample size purposively selected consisted of 137 students from four schools in Education District II and IV, Lagos State, Nigeria. Two hypotheses were raised and tested at 0.05 level of significance. The collected data were analyzed using t-test. The result of the analysis revealed that cooperative learning strategy enhanced the low ability students’ achievement in Mathematics. Also, cooperative learning strategy enhanced low learning abilities students in understanding mathematics irrespective of their gender. It is therefore, recommended that teachers should adopt the cooperative learning strategy to teach Mathematics. For teachers to be more conversant with the use of cooperative learning strategy, as well as other interactive methods of teaching mathematics, workshops and conferences should be organized for secondary schools on the use of different methods of teaching learners from different ability levels, especially cooperative learning strategy.