Correlations between various marks in English and in mathematics (taught in English) were computed for a single cohort of Chinese-speaking students in a Macau secondary school throughout their six years of study there. The correlations changed over time, and in general they declined. A naive theory that only a certain threshold level of English competence is necessary for success in mathematics was not supported by the finding that among the students with higher English scores, the English-mathematics correlations were much higher than among those weaker in English.