A sound education in mathematics is important for any modern knowledge based economy. Mathematics is now important in many areas where it has not previously played much of role, for example, in biology, social sciences etc. If the proper mathematical foundations are not laid during the formative years of childhood and adolescence, it becomes increasingly difficult to address this weakness in later life. The attempts to confront these shortcomings during retraining in later life are generally wasteful and only partly successful. The present study was designed to investigate the comparative effectiveness of problem-solving approach on the academic achievement of secondary school students in mathematics. The major objectives of the study were: (1) To determine whether the problem solving approach is more effective than expository strategy of teaching on academic achievement of students in mathematics. (2) To determine whether the problem solving approach is more effective than expository strategy of teaching on attitude of students in mathematics. (3) To examine the effect of problem-solving approach on the academic achievement of low achievers. (4) To measure the effect of problem-solving approach on the academic achievement of high achievers. (5) To find out the effect of problem-solving approach on the retention of students in mathematics. To achieve the objectives of study, following null hypotheses were tested: (1) There is no significant difference between the pre-test mean achievement scores of experimental and control group. (2) There is no significant difference between the pre-test mean achievement scores of low achievers of experimental group and control group. (3) There is no significant difference between the Pre-test mean achievement scores of high achievers of experimental and control group. (4) There is no significant difference between pre-test mean attitude scores of experimental group and control group. (5) There is no significant difference between the post-test mean achievement scores of experimental group and control group. (6) There is no significant difference between post-test mean achievement scores of low achievers of experimental group and control group. (7) There is no significant difference between post-test mean achievement scores of high achievers of experimental group and control group. (8) There is no significant difference between post-test mean attitude scores of experimental group and control group. (9) There is no significant difference between mean achievement scores of experimental group and control group and control group on retention test. (10) There is no significant difference between mean achievement scores of high achievers of experimental group and control group on retention test. (11) There is no significant difference between mean achievement scores of low achievers of Experimental group and control group on retention test. Secondary school students studying mathematics constituted the population of study. The student of 10th class of Govt. Pakistan Girls Higher School, Rawalpindi (Pakistan) was selected as a sample of the study. The pre-test post-test equivalent- group design was used for the study. The sample size consisted of forty eight students who were divided into experimental group and control group, each consisting of 24 students by equating them on their previous knowledge in mathematics, as determined through a pre-test. A treatment of planned problem-solving approach was provided to the experimental group while the control group was taught by expository strategy for a period of six weeks.