In a multilingual context, this study investigates the role on mathematics achievement of the provision of instruction in the home language. It compares characteristics of 5048 Grade 6 learners in 275 Namibian schools. The outcome variable is the standardized SACMEQ mathematics score collected in year 2000. Hierarchical linear modeling is used to partition the total variance in mathematics achievement into its within- and between-school components. The results do confirm the significant role of low language skills on the overall low mathematics scores, which may question the effectiveness and equity of the current bilingual policy.