This article presents a study, which examined the effectiveness of a specially designed intervention on chemical changes. The participants were one hundred and thirty Greek primary school teachers. The results show that pre-intervention, teachers were found to have a relatively limited ability in explaining chemical changes. The teachers also held a number of misconceptions similar to those of pupils. Post-intervention, teachers’ descriptions and explanations were found to be significantly improved. However, post-intervention, teachers seemed better able to manage the combustion of hydrogen and the heating of sugar, than the burning candle which had been studied in the course.