The study investigates the rationale and value of using cooperative learning strategies in the mathematics classroom with special reference to its effectiveness in promoting problem solving skills and levels of achievement in mathematics. In this it is compared with traditional teaching methods. The study sample was composed of 348 eighth grade students in eight classes from two separate female and male schools and included female and male teachers. Two female and two male teachers were trained in the use of cooperative learning strategies in their classes during the implementation of the experiment, while the other four teachers had been asked to keep using their usual traditional teaching methods. The experiment took place within two scholastic semesters and the same mathematical content was covered by the two groups within the experiment. Pre- and post-mathematical achievement tests were employed to assess students' progress in achievement and problem solving skills. Also, a programme evaluation questionnaire was applied at the end of the experiment for all students involved. In addition to the quantitative methodology, the study also addressed qualitative issues. All the teachers involved in the experiment, and a sample of students, were interviewed. Lesson observations were conducted within the research programme to evaluate the implementation of the cooperative learning strategies and teachers' and students' responses towards it. In addition, teachers were asked to record weekly diaries to assess their judgement on student progress within the experiment. The researcher recognises that teachers and students who apply cooperative learning strategies might be strongly motivated and be more enthusiastic by the very fact of trying a new strategy. Consideration was, therefore, given to this point at all stages. The study tries to determine if such strategies are really valuable in the mathematics classroom, allowing for all the variables, and have measurable effects in promoting problem solving skills and achievement in mathematics. The study demonstrates that cooperative learning strategies enhance the teaching and learning process by transferring focus from a teacher-centred situation into a student- centred learning context. This enriches the cognitive, competitive and social interaction and, hence, develops outcomes in the cognitive, affective, motivational and social domains. The study proved the positive impact of applying such strategies in enhancing mathematical achievement and promoting problem solving skills compared with the impact made by traditional teaching strategies. Cooperative learning strategies could offer all students with different abilities the opportunities to cooperate, interact and participate in the mathematics lesson. This gave them a chance to do mathematics by themselves, speak their thoughts, offer and receive explanations, introduce several procedures for solving problems and, hence, profit from the mathematical knowledge available in the group as a whole. The new learning approach encouraged students to challenge problems and provided them with the opportunities to speak mathematically, to understand the mathematical concepts and rules and to use them. Results from the study also demonstrated that cooperative learning developed other skills. It improved student interaction, communication and social skills and built more positive attitudes towards learning compared with the traditional methods. Developing student behaviour and personality was, therefore, an important additional feature. The study illustrated that cooperative learning strategies help to solve problems faced by teachers in classroom management. As expected, the research showed that outcomes differed from case to case and from one situation to another. The academic ability of students and the quality of mathematical material played an obvious role emphasising positive or negative affects. On the other hand, gender differences examined in the study showed that, despite female students achieving better results, male students actually displayed more positive attitudes toward mathematics. But again, female students were more enthusiastic in applying cooperative learning. The study is the first of this nature to be applied in Jordan and has several implications for theory and practice. No teaching method is the best, but it is recommended to provide teachers with professional training programmes to apply more developmental teaching methods effectively and to modify mathematical textbooks and teachers' guides for the use of different teaching methods. It is recommended that more research be carried out in different fields of study to concentrate on improving the quality of learning and enhancing problem solving skills.