Contemporary school learning typically includes the processing of popular scientific information as found in journals, magazines, and/or the WWW. The German high school curriculum emphasizes that students should have achieved science literacy and have learned to evaluate the substance of text-based learning content by the end of high school. Alongside the content of science-related information, two issues are important when students gauge its substance: (a) information about its source, such as whether an expert has provided it (attribution shields) and (b) its wording, for example, whether so-called markers of tentativeness such as "probably" point to a preliminary assessment (plausibility shields). Based on the outcomes of a content analysis of the usage of such shields, we report an experiment that varied the occurrence of both types of shields in single arguments. Results showed effects of both manipulations on the perception and evaluation of arguments. However, information about the source impacted more strongly on the evaluation than the wording. We relate this finding to the formulation of as well as students' processing of text-based learning content and suggest practical implications for teaching students how to handle scientific information.