Online news literacy training has been so far insufficiently conducted and evaluated, and even less so with younger news consumers. Against the backdrop of online news cognitive processing, interventions against misinformation, and inquiry-based learning, we designed, conducted, and evaluated a pilot online news literacy training with 36 elementary school students from Germany. In a causal comparison, quantitative data from N = 29 students attest high participant acceptance and substantial effects of the inquiry-based training on participants' ability to correctly assess online news credibility, and on the corresponding cognitive processing route, moving this from intuitive to analytic processing. Despite the small sample, the experiment was only underpowered regarding the between-subject effect, whereas the power was sufficient for all other effects. These encouraging findings of the pilot training may be the result of knowledge reorganization associated with inquiry-based learning. Further educational research and practice are needed to understand the efficacy of the training at scale.