Effects of Differentiated Instruction on Learner Achievement in Mixed-Ability Classrooms: A Quasi-Experimental Study

Abstract

The diversity of learners in contemporary classrooms has placed increasing pressure on teachers to adapt instruction to varied readiness levels, interests, and learning profiles. Differentiated instruction has been widely advocated as a pedagogical response, yet rigorous experimental evidence of its effectiveness in mixed-ability classrooms remains limited, particularly in mainstream public-school settings. This study examined the effect of differentiated instruction on learner achievement in mixed-ability classrooms in junior secondary schools. A quasi-experimental, non-equivalent control group design with pre-test and post-test measures was employed. Two intact Grade 8 classes (N = 78) were assigned to an experimental group exposed to a six-week differentiated instruction program and a control group taught through conventional whole-class instruction. Achievement was measured using a researcher-constructed test validated by experts and pilot-tested for reliability. Independent-samples t tests, analysis of covariance (ANCOVA), and effect-size estimation were used to analyze the data. The experimental group recorded significantly higher post-test scores than the control group (F(1, 75) = 28.41, p < .001, partial η² = .27, d = 0.94), indicating a large practical effect. Gains were strongest among low-achieving learners, suggesting that differentiated instruction narrows performance gaps in mixed-ability classrooms. Implications for instructional planning, teacher preparation, and curriculum policy are discussed.