In this article, a series of activities on explicit teaching of specific aspects of the 'nature of science' are presented. The authors explore teaching the nature of science through inquiry-based activities on electric circuits. The activities concern classification of objects as conductors or insulators and took place in three classes of 4th grade (ages 9-10) students in a primary school in Thessaloniki, Greece. The purpose was for students to find out that the same, limited, observations could result in different choices of classification criteria, depending on individual creativity and imagination. It was also hoped that the students would see that the criteria might change with evolution in technology and new instruments leading to new evidence, or because old evidence is reinterpreted.