Most students profit from the easy accessibility of online information, but specific competencies for successful reading on the internet are seldom taught during class. Therefore, students might not be able to choose credible information autonomously. Empirical evidence suggests that high school students hardly evaluate the credibility of sources (“sourcing”) when reading multiple documents. Consequently, effective interventions which foster sourcing skills are needed. This study evaluates the effects of a written instruction designed to augment sourcing activities in a multiple document reading task by inducing epistemic vigilance. The written instruction introduces the concept of the division of cognitive labor and informs about low editorial control on the internet. In comparison to a control group, students receiving the instruction prior to completing an internet research task showed more attention to, evaluation of, and memory for sources