The study examines science-related course choices of high-school students in the culturally diverse schools of the province of British Columbia, Canada. The analysis employs K-12 provincial data and includes over 44,000 students born in 1990 who graduated from high school by 2009. The research sample reflects the presence of about 27% of students for whom English is not a first language. We construct an empirical model that examines ethno-linguistic and gender differences in Grade 12 course choices while accounting for personal and situational differences among students. The study employs a course selection typology that emphasizes readiness for science, technology, engineering and math fields of study. Findings indicate that math- and science-related course selection patterns are strongly associated with ethnicity, qualified not only by gender and prior math and science achievement but also by the individual's grade level at entry to the system and enrollment in English as a Second Language program. Students who are more likely to engage in math and science courses belong to Asian ethno-linguistic groups and entered the provincial school system during the senior high-school years. We suggest that ethnic diversity and broader academic exposure may play a crucial role in changing the gender composition of science classrooms, university fields of study and science-related occupations.