Background: Children have been shown to hold misconceptions about illness, and previous work has indicated that their knowledge can be improved through the use of interventions. Aims: This study aims to evaluate interventions based on the provision of factual information for improving understanding of contagious illness. Sample: The participants were 96 children from two age groups: 7 and 11 years. Methods: During the pre-test, the children were asked about three contagious illnesses and one novel illness. There were three intervention conditions, differing in the level of factual information provided: explanations provided, no explanations provided and scientific factual style. The interventions were focused on contagious illnesses (cold, chickenpox). A post-test was conducted 6 weeks later. Results: Results from the pre-test show that the older children have more sophisticated understanding of illness than the younger children. Mean pre- to post-test change was calculated and analyses revealed that there is greater pre- to post-test change in the explanation and scientific fact conditions when compared with that in the no-explanation condition. The improvements in knowledge generalized to other contagious illnesses, and the older children showed more improvements than the younger children. Conclusions: These findings add to the literature on children's understanding of contagious illnesses and contribute towards discussions on the best approach to health education.