The status of African languages in the education system is a socio-political concern in post-independence Namibia that is typified by multilingualism and ethnolinguistic contentions. While the discrimination against the African languages is eminent, there is very little scholarly work that  illuminating on forms of discrimination associated with African languages in science assessments, particularly within Namibia which has a history of a brutal colonialism.  As a result, there is an English only policy for all written assessments as from Grade 4 and beyond. However, the linguistically diverse learners   do not always meet the requirements for the Standard written English required  in  their science written assessments , and this might have devastating consequences for learners’ ability to perform well throughout their entire school careers. To date, Namibian Language-in-Education Policy continues to privilege monolingual approaches to language use in the classroom and delegitimize the use of minoritized languages and language practices in education. In this study, I highlight the historical legacy of monolingual language ideologies and discuss the detrimental effects which arise when Namibian indigenous  languages are not welcomed within the education system. Using Bakhtinian concepts of heteroglossia as well as translanguaging and trans-semiotising , I focus on the multilingual and multimodal ways in which the science teacher makes science meaning in classroom discourse. I then trace the children’s appropriation of these meanings in their formal written science assessments. My data analysis contrasts the heteroglossic and multimodal meaning-making of classroom discourse with the monolingual and monomodal requirements of formal assessments, showing how the latter are not valid indicators of the children’s understanding of science concepts. I highlight the ways in which the heteroglossic and translanguaging practices could represent a positive shift to the way in which multilingual language practices are talked about and can contribute to decolonising language policy in  Namibian context.