Neurofeedback training (NFT) provides strategies for children with ADHD to achieve changes on the neurophysiological and behavioral level to attenuate ADHD symptoms. We assume self-efficacy (an “active attitude”), a core variable in successful NFT. In a randomized, double-blind controlled study, we investigated the impact of a “placebo instruction” on the EEG-regulation performance during two ... [Show full abstract] sessions of Theta-Beta-NFT in children with ADHD (age 8–12 years). Children receiving the information “this might be a placebo-training” showed inferior neuroregulation (n = 10) compared to children receiving a standard instruction (n = 12). Results of our pilot study are discussed in view of factors necessary for a valid training (ensuring maximal self-efficacy in the participants) and the fidelity of placebo-controlled trials in NFT-research.