We present an empirical investigation of a classroom training fostering vocational students' consideration of source information when deciding about science-based controversies. The training was specifically aimed at raising students' awareness of the division of cognitive labor and the resulting need to take a source's competence into account when deciding whom to trust. Data were collected from a training group and a waiting list control group in a pretest-posttest design. The results show that students benefitted from the training in terms of their inclination to agree with pertinent expert sources rather than low-pertinent experts and to refer to the source of information to justify their judgment. Source memory was not affected by the training.