It has been observed that the low academic performance of trainees at the Windhoek Vocational Training Centre has been on the increase at an alarming rate without any proven reasons Malwa (2018). This may be the case in other vocational training centres. Thus, this study examined the influence of English as a Second Language on trainees' academic performance at Eenhana Vocational Training Centre in Namibia. The study, therefore, tried to answer these questions; (a) What factors in English influence trainees' academic performance? (b) How did the influence of English as a Second Language and medium of instruction affect other subjects? (c) How did the trainees comprehend their academic work? '.This is a qualitative study which used the snowball sampling method to select 5 trainers and 10 trainees as participants.'. The data were collected through face-to-face interviews, participants observations and document examinations. Narrative and thematic analysis were used in analyzing data. The study revealed that the performance of trainees in their academic work is determined by their ability to understand English as a Second Language. Their proficiency level in English influences how best or poorly they can perform in their academic work. It was also found that trainees who have poor English language proficiency find it difficult to understand their subjects content and also performing their best in academic work, while those who are good at the language perform well academically as they can understand what they are learning and they can handle the assessment activities appropriately. The study will inform the Higher Education policymakers, trainers, and trainees as it enhances an understanding of the influences of English as a medium of instruction on other subjects for them to employ the best teaching and learning strategies such as Access or bridging courses to improve the problem caused by the language barrier.