The purpose of this study was to better understand how middle school students consider the source of information when processing videos with conflicting information. To this end, we exposed a sample of seventh-graders to a series of videos in which two interviewees expressed divergent positions on a socioscientific issue ('Will organic farming be able to feed the entire world population by 2050?'). After viewing the videos, students were asked to recall the sources they had seen and indicate how far they had perceived the sources to be credible and convincing. Results showed that students paid close attention to the information given about the sources during viewing and rated their credibility accordingly. However, only a minority of students rated the expert sources as the most convincing after viewing the videos, while students' beliefs on the topic contributed to source evaluation. These results suggest that although middle school students may pay attention to the identity of sources when viewing a video, they are unlikely to use this information to assess the reliability of the message. [Spanish translation by Mercè Rius.]