The dominant role of English as the global language of science entails a requirement for science teachers to equip their non-native English-speaking students with receptive and productive language skills for communication in scientific contexts. Although science courses with English elements are part of some schools' bilingual programmes, they are usually not available to a wider student audience, but are restricted to high achieving or highly motivated students. The present study was to test whether a newly developed biology content and language integrated learning (CLIL) unit could also benefit standard ninth grade classes. The learning gains and motivation of bilingually inexperienced students were compared to those of a preselected group and a comparison group that had been taught solely in their native language. All participating classes achieved similar gains in content knowledge, and the standard students rated their motivation for bilingual science lessons as positive, albeit not as high as the preselected group. We thus provide evidence against concerns that teaching non-selected students bilingually might lead to deficits in content knowledge acquisition. Following this, we conclude that scientific English should be a part of standard science lessons regardless of specific school programmes.