This study investigated the Effect of Case-based Strategy on Academic Achievement in Mathematics Word Problems among Junior Secondary School Students in Ibadan Metropolis, Oyo State, Nigeria. The research focused on evaluating learning outcomes, knowledge retention, and overall students’ performance when exposed to this teaching approach based on constructivism and behaviorism theories of learning. The study employed a quasi-experimental research design. The population of the study consisted of all 20244 Junior Secondary School students in Oyo State, while two intact classes of 68 JSS2 students participated in the study. Two lesson plans and a validated Mathematics Achievement Test (MAT) were used as instruments for data collection. The MAT was tested for reliability having a value of 0.85 and the data generated was statistically analyzed using frequency counts, percentages, standard deviation and Analysis of Co-variance (ANCOVA) at a significance level of 0.05. The findings revealed that the effect of case-based strategy on students’ academic achievement was significant (F(1,65) = 72.771, p< 0.05) and was found to be more effective in enhancing students’ academic achievement in algebraic word problems. It was recommended that educators should incorporate case-based strategies in teaching Mathematics Algebraic word problem at the Junior Secondary School for effective outcome.