The Maltese National Minimum Curriculum published in 1999 sought to strengthen bilingualism by reinforcing the practice of teaching and assessing some subjects in English and others in Maltese. It also pointed out that code-switching should only be used in cases of severe pedagogical difficulties. As a new National Curriculum Framework was being prepared some educators suggested language as a possible barrier to student progress and argued that the traditional practice of teaching subjects such as science in English should be reconsidered. This study investigated language choices, function and code-switching in science lessons. Classroom observations, interviews and focus groups showed that in state schools 12-13 year old students were being taught science predominantly in Maltese while reading, writing and formal assessment were in English. Students who were more exposed to English, irrespective of class stream, used this language more frequently than those who were less exposed to the language. The findings seem to suggest that teachers may be overcautious. While code-switching may initially provide technical terms and serve as a bridge between the two languages, eventually it can give way to a more precise and formal use of English thus ensuring both learning of science and development of bilingualism.