This article examines the use of the national language, Setswana, as the language of instruction in linguistically and ethnically complex primary schools in Botswana, and the dilemmas it presents. The current language-in-education policy in Botswana requires the use of Setswana as a language of instruction at standard 1 in public schools. The study used the qualitative approach, with teachers as implementers of the policy being the key participants. The study used open-ended questionnaires, interviews, classroom observations and field notes to elucidate the complexity involved in the interpretation and translation of such a policy in schools which children with different home languages attend. These included foreigners, immigrants and Setswana-speaking children who have been through preschool education. The findings indicate that there is tension between standard 1 classroom practices and what the policy stipulates. The use of Setswana has a profound negative impact on ethnically diverse standard 1 classes because it presents challenges to effective teaching and learning.