This paper investigated how vocabulary knowledge is an essential variable for academic achievement during the post-COVID-19 era in Grade 10 learners. Among many variables of poor performance in Grade 10 is inadequate vocabulary in First Additional Language. This paper is underpinned by Vygotsky’s socio-cultural theory which advocates that language learning occurs through interaction with more knowledgeable others. The present study is quantitative, in which a vocabulary size test (VST) and a productive vocabulary test (PVLT) were administered to 84 conveniently selected participants. This paper revealed that learners have very limited vocabulary knowledge and this affects academic achievement. In addition, COVID- 19 worsened the situation since social interactions were limited, thereby impeding language development. The authors argue that in order for post-COVID-19 learners to cope in the academic world, strengthening vocabulary knowledge is key to equipping these learners with the required skills to cope with virtual learning. Some of the essential skills for learners to learn online include reading, writing, listening and speaking skills. These skills would assist learners in communicating their needs, discussing solutions and expressing themselves when the need arises. This paper recommends using explicit vocabulary instruction to improve learners’ academic achievement in the post-COVID-19 era. The Department of Basic Education should train teachers on how to design fun vocabulary activities online. For instance, quizzes, the Frayer model and other virtual word activities. Keywords: Academic achievement, Explicit vocabulary instruction, Rich language contexts, Post-COVID-19, Vocabulary knowledge