Taking into account (German) students’ deficiencies in scientific literacy as well as reading competence and the ‘mother tongue + 2’ objective of the European commission, a bilingual course on molecular biology was developed. It combines CLIL fundamentals and practical experimentation in an out-of-school lab. Cognitive and affective evaluation of 490 students from upper secondary schools followed a quasi-experimental design, including two experimental (bilingual course and monolingual course) and one control group that did not take part in any of the courses. Cognitive achievement concerning molecular biology and self-concept were measured in a pre, post, follow-up test design. The study has shown that cognitive achievement concerning biological content knowledge of students having participated in a bilingual course (English and German) does not differ significantly from cognitive achievement of those that have participated in a monolingual course (German). Regarding biological self-concept, no significant differences between students having assessed themselves as being rather interested and talented in foreign languages and students having assessed themselves as being rather interested and talented in science could be observed. This indicates that bilingual courses in an out-of-school lab are equally beneficial for both of these groups.