Critical thinking is a fundamental skill that all citizens should have. Unfortunately, while beliefs in unfounded claims are pervasive, teaching critical skill is a strenuous task. Digital mobile interaction could potentially support face-to-face teaching to foster critical thinking skills. In this paper, we present a preliminary version of the BaloneyMeter, a mobile app that provides support for teaching critical thinking skills. We report on a case study in a class of 150 students and present an open research question that we plan to address in subsequent work.