The purpose of the study was to compare the effectiveness of cooperative learning strategy and Traditional instructional method on pupils' academic achievement and their motivation to learn in the physics classroom at Chibote Girls Secondary School in Kitwe District of Zambia. The research was a Pre-test- post-test control group design. The population of the study consisted of 625 Grade Eleven pupils studying at Chibote Girls Secondary School in Kitwe District and the Five (5) teachers teaching physics subject at the school. A sample 60 pupils and two (2) teachers were used for the study. Simple random sampling was used to select the teacher to teach the Traditional instructional method (control) class and convenience sampling was used to select the teacher to teach the cooperative learning (experimental) class. Pre- and post- motivation survey questionnaire of the five point Likert scale of strongly agree to strongly disagree and pre- and post- tests were used for data collection. The motivational survey questionnaire was face and content validated while the tests were drawn from standardized past physics examination questions of the Examination Council of Zambia. The reliability for the pre- and post-motivational questionnaire survey was determined using the Cronbach's Alpha reliability method. The reliability coefficient of 0.334 and 0.901 was obtained for premotivational survey and post-motivational survey respectively. Factor analysis was carried out on the pre- motivational questionnaire survey and the communalities of the items on the pre- motivational survey ranged from 0.438 to 0.854 an indication that all the items on it were reliable. The two motivational questionnaires were therefore, used for the research. The data collected were coded and analysed using the Statistical Packages for Social Sciences (SPSS). The one way Analysis of Variance (ANOVA) and Univariate Analysis of Variance and ANCOVA were employed. The study revealed that the use of Cooperative learning strategy do improve pupils' academic achievement as well as pupils' motivation to learn than the Traditional instructional method. Therefore, it is evident that Cooperative learning strategy is more effective in the teaching and learning of physics than Traditional instructional method.