This study investigated the effect of mother tongue instruction and gender on second language acquisition using a causal-comparative quantitative research design. The two distinguishing groups compared were (i) learners that were taught in their mother tongue (Afrikaans) and (ii) learners that were not taught in their mother tongue but in English, from grades 1 to 3. The dependent variable was the second language acquisition that was accounted for by the learners' performance in grade 5 in three tests: a vocabulary, a syntax and an oral communication test. The sample included 2 schools in Windhoek and a total of 70 learners, with 35 learners that had Afrikaans as medium of instruction, and 35 learners that had English as medium of instruction from grades 1 to 3. The study aimed to shed some light on the ongoing debate as to whether mother tongue instruction or immersion in L2 is more beneficial for the child's second language acquisition and competence. Although clear differences between the two language groups were found with regard to their English proficiency in grade 5, these differences were not statistically significant. With regard to gender, clear differences were also found and most of these differences were statistically significant.