This study investigated the effects of Diglossic language as medium of instruction in student's physics achievement. It assessed the physics achievement of the students before and after the intervention. It ascertained whether the use of Diglossic language compared to the use of Pure English language had a significant effect on students’ achievement in physics. It employed the match-only pretest-postest group quasi-experimental design using 70 students in a public high school divided into two groups, with 35 students in each group. The diglossic group was taught using the mother tongue and English language (70% mother tongue and 30% English) while Pure English group was taught using English language only. A validated teacher-made achievement test in physics was used to measure the physics achievement level of the students before and after the intervention. Mean and standard deviations were the descriptive statistics employed. The t-test for dependent and independent samples were employed as inferential statistics. Results revealed that students in both Pure English and diglossic groups had low level of achievement in physics before the intervention. The students in Pure English group had an average achievement level in physics, while those in the diglossic group had a high achievement level in physics after the intervention. Results showed that Diglossic language significantly influenced the achievement level of the students. Students taught in Diglossic language gained a higher level of physics achievement and understood better the physics concepts compared to students taught in Pure English language.
Diglossic Language, Classroom instruction, Pure English, Physics Achievement
