School is a subculture of any society having different educational diversity. This diversity affects on teachers and students achievements; pillars of teaching learning process. Teachers have great concerns towards students’ success. They deliver plethora of information to improve students’ achievements. Present quantitative ex-post-facto research was framed to explore the effect of teachers’ self-efficacy on students’ achievement scores applying multilingual instructions for students’ success on sample of randomly selected 1100 male respondents; 300 secondary school teachers and 800 students of District Kasur, of Lahore Division. Data from teachers were collected by administering long form of Teachers’ Self-Efficacy Scale whereas students’ achievement scores were obtained from annual gazette notification of Board of Intermediate and Secondary Education, Lahore. Cronbach’s Alpha Score was applied to confirm instrument’s reliability .851. Normality of the data were confirmed by calculating Shapiro-Wilk’s test. Findings of regression analysis depict that overall teachers’ self-efficacy has affected 65 % whereas students’ engagement 59 %, educational strategies 60 %, classroom management 59 % and teachers’ medium of education has affected 30 % on students’ achievement scores. Present research recommends that Government structure teachers’ self-efficacious believes through providing training, conducting workshops before joining teaching professions and ensuring certificates; once teachers’ confidence structure, less possible to alter to obtained desired achievements during teaching learning process. Furthermore, it is dire need to implement single medium of instructions; English / Urdu in public sector secondary schools of Punjab as bilingual medium of education have been remaining one of the barrier that lead students towards poor achievements.