Student teachers were tested before and after a teaching unit on electrostatic interactions in an attempt to consider their intuitive ideas and concept development. A study was made of students' explanations of basic interactions: those between two charged bodies, and those between a charged body and a neutral body. Two indicators of the cognitive status of the explanations were investigated: "context dependence" and "certainty or confidence index". This allowed cognitive comparisons to be established between the explanations of different electrostatic interactions, and between the degrees of difficulty they represent for satisfactory conceptual evolution. The greatest difficulties were found with explanations of the phenomena of electrostatic induction. The sample consisted of 52 students in primary school teacher education who participated in a teaching unit designed to overcome these obstacles. (Contains 2 tables, 10 figures and 2 notes.)