This paper reports on part of an evaluation of a 2-year program providing preparatory support for 430 Cantonese Chinese-native-speaking students switching from Chinese to English-medium instruction late in their secondary schooling, mainly because of aspiration to English-medium tertiary study. Focusing quantitatively and qualitatively on scientific English achievement, the paper addresses the content or cognitive-academic dimension, so far as underrepresented in English-as-foreign-language research, as is senior secondary school immersion itself. While no direct cause-effect relationship between the program and achievement levels was to be claimed, the observed differences between program participants and non-participants were ultimately minimal. Reasons proposed for the intervention's outcome seemed mainly related to key stakeholders' apparent limited awareness of cognitive-academic language and its development. The discussion identifies factors arguably crucial for support programs for senior secondary school academic study through English-as-foreign-language. (Contains 4 tables.)