The article deals with questions as to how Secondary School children begin to understand the meaning of moral notions within the »deception — veracity« sphere, and how they form moral ideas about these phenomena. It is based on material gathered as a result of research carried out with 253 pupils. The research was based on definitions of such moral notions as deception, cheating, veracity, subterfuge, shamming, sincerity, confidence and the like. The article shows how children from 12 to 15 years of age gradually grasp the phenomena expressed by the above notions, and comes to the conclusion that children of just that age give so much attention and thought to these phenomena that they are able to call them correctly and point out their characteristic features. Besides the aspect of development, the article briefly mentions also the concrete meaning and content of four of the above-mentioned notions. From the result of the research conclusions are drawn with regard to pedagogical practice.