The study investigated the effects of utilising English as the primary teaching language on the academic development of Grade 4 (Gr4) learners, specifically focusing on the Life and Living (L&L) component of Natural Sciences (NS). Gr4 learners commonly transition to English as the Language of Learning and Teaching (LoLT), relegating native languages such as Sesotho to mere study subjects. This shift often results in comprehension and retention challenges, hindering students' academic achievements. By employing a quasi-experimental research design, the study used a purposefully selected sample of 80 Gr4 students from two primary schools. The control group (45 learners) received English instruction from Grade R to Grade 7, while the experimental group (35 learners) switched from Sesotho to English in Gr4. Both groups underwent pre-tests and post-tests, revealing statistically significant differences favouring the experimental group. These findings support the research hypothesis that introducing English as the LoLT as early as Grade R has a significant impact on learners' performance, particularly in NS. It is recommended that English be adopted as a medium of instruction for NS, as this better prepares students for future academic challenges.