In a multilingual context, this study investigates the role of language skills on mathematics achievement. 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 positive correlation between strong language skills variations at the school-level and low pupil mathematics scores, which may question the capacity of the current bilingual policy to provide for an effective and equal learning environment.