The study was aimed at establishing the effect of English Language Proficiency on Junior Secondary School Students’ Performance in Mathematics. Solomon Four Group design was used as a research design for the study. The target population comprised of junior secondary school students in Bauchi Southern educational zone of Bauchi State, Nigeria, Purposeful sampling technique was used in chosen the four boarding schools for the study. The exact number of JSS2 students found in each school formed the sample in the study. Data from the students achievement test (MWPST) was coded and analysed using Statistical Package for Social Sciences (SPSS) version 17. Analysis of Variance (ANOVA) and independent t-test were used to test the research question at 0.05 level of significant. Analysis of data generated from students pre-test revealed that, the effect of English on students’ performance in word problems was insignificant (t (203) =0.919, p>0.0). The result from the study showed a significant difference (F (417) =48.63, p=0.00, p<0.05) in the effect of English language on performance between the four groups in the post-tests. The study posits that the interventional strategy (Mathematical modelling) significantly improves the performance and problem solving abilities. Overall results in this study illustrate that students’ performance in word problems increased significantly. The result also indicated an increased in their proficiency of the language of instruction and text language increased. In essence therefore learners’ performance seem to be directly related to language use in the mathematics classroom.