Bilingual education could solve many challenges introduced by an increasingly internationalised education system. Content and Language Integrated Learning (CLIL), in particular, may equip students with the necessary cultural and communicative skills to succeed in today's academic environment. However, it is not yet clear how CLIL can be employed effectively in short-term educational contexts where full-term bilingual programmes are not feasible. We designed and assessed a one-day CLIL module for ninth graders at our university's gene-technology lab. The assessment of our module with 252 grammar school students indicates that a CLIL module does not achieve the same learning success as an equivalent non-CLIL module. Even with additional language scaffolding material, full access to online dictionaries, and the availability of crucial workbook passages in their native language, CLIL students could not achieve the same short-term content learning success. We consequently argue that more attention should be paid to the inherent trade-off between language and content learning when carrying out short-term CLIL programmes. Moreover, we caution against using only content and language scaffolding to mediate this trade-off.