This study sought to determine the effect of the problem-solving approach on academic achievement of students in mathematics at the secondary level. The secondary school students studying mathematics constituted the population of this study. The students of 10th class of Government Pakistan Girls High School Rawalpindi were selected as a sample for the study. Sample size consisted of 48 students who were equally divided into an experimental group and a control group on the basis of pre-test. Treatment of the planned problem-solving approach is the guideline of Sherreen (2006) and Polya's (1945) heuristic steps of the problem-solving approach. After the treatment, post-test was used to see the effects of the treatment. A two-tailed t-test was used to analyze the data, which revealed that both the experimental and control groups were almost equal in mathematics base at the beginning of the experiment. The experimental group outscored the control group significantly on the post-test.