The study investigated the "effect of instructional materials on senior secondary students' achievement in Economics. The study adopted the quasi-experimental design in the sense that the subjects were not randomly assigned into groups. The simple random sampling technique was used to obtain the sampled schools. Sixty (60) students consisting of 30 assigned to experimental group and 30 were assigned to the control group. Intact classes of SS II economics students from schools in Pankshin local government area of Plateau state. The instrument used for the collection of data for the study was titled: "Economics Objective Achievement Test" (EOAT).which was developed by the researcher. The instrument was validated by three experts; One in Economics and two from measurement and evaluation who validated the instrument in term of clarity, content and coverage. The reliability of the instrument was determined using the Kuder-Richardson (K-R 20) which yielded a reliability co-efficient of 0.76. The mean and standard deviation were used to answer the research questions while the t-test statistics was used to test the hypothesis at 0.05 level of significance. The findings revealed that the cognitive constructivist model was better than the conventional method in enhancing students’ achievement in economics. Thus, economics teachers should be trained on how to employ this teaching model to improve the quality of economics instruction for better performance of students' in both internal and external examinations in economics
