This mixed-methods (QUANT-qual) study compares test performances of two classes of 52 (26 in each class) Grade 5 learners in a multiple choice Maths test written in English language (Group A) and the same test but with questions written in Shona language (Group B), respectively. The paper also examines the role of language in the development of attitudes and fear of mathematics by learners at the same primary school in Gokwe district, Zimbabwe. Results showed that there were significant differences (in favour of the English language) between Group A’s performance and Group B’s performance. Other findings were that teachers had mixed feelings towards the use of mother tongue in teaching and learning primary school mathematics, but generally agreed that the language of instruction and/or learning affect performance in mathematics, attitudes towards mathematics and fear of mathematics. The paper concludes that using mother tongue as a medium of instruction in the teaching of mathematics in the Zimbabwean junior primary schools is desirable but the feasibility could not be established. It is recommended, among other things, that there is need for further research and policy formulation on the language of learning/instruction at various school levels in Zimbabwe.