The study aimed at checking the existing level of understanding of concepts in the subject of Chemistry among Class IX students and to investigate the effectiveness of concept formation teaching model over traditional method on Class IX students’ achievement. It was an experimental study in which concept formation teaching model was compared with traditional method. A sample of 460 students (300 Boys and 160 girls) were selected from nine Government High Schools for Boys and Girls of Rawalpindi city for administering an achievement test to measure the existing level of understanding of concepts in the subject of Chemistry among Class IX students. For experiment, sample size was 290. One hundred and forty three students in experimental groups and one hundred and forty seven students in controlled groups were selected because the classes were taken “as is”. Pre-test-Post-test Nonequivalent-Groups Design was used. The students of experimental and controlled groups were taught concept formation teaching model and traditional method respectively for three months. Pre-test and post-test were administered to experimental and controlled groups at the beginning and end of the experiment. 31 lesson plans were made on the format of direct instruction from chapter No. 7 to 10 of Chemistry textbook for Class IX published by Punjab Textbook Board. To determine the effects of concept formation teaching model on achievement of Class IX students in the subject of Chemistry, the significance of difference between the mean achievement scores of experimental and controlled groups was tested at .05 level by applying t Test, Product-Moment Correlation and analyses of covariance. Data analysis reveals that existing level of understanding of concepts in the subject of Chemistry among Class IX students was not up to 50 percent. The students of experimental and controlled groups were equal in pre-test at the beginning of the experiment. The experimental groups outscored significantly the controlled groups on post-test showing the supremacy of concept formation teaching model on traditional method. Hence the ultimate results of the study indicated that concept formation teaching model was more effective as compared to vtraditional method. Furthermore, concept formation teaching model appeared to be favorable for both boys and girls for the understanding of Chemistry concepts.