Background Transitioning a child prematurely from a booster seat to the vehicle seat with seatbelt is prevalent worldwide. This type of inappropriate restraint use can worsen the severity of injuries of children in a motor vehicle crash. Despite the availability of the 5-step test (a tool to aid parents in making transition decisions), there is a lack of research on its effectiveness in changing practice. The objective of this study was to evaluate the effectiveness of the 5-step test.

Methods To assess the 5-step test, a randomised controlled design was employed. The study compared parents exposed to the 5-step test (intervention group) vs. legal requirements (control group). All resources were provided in written form. After exposure, parents were asked to evaluate the suitability of an adult seatbelt when observing their child (aged 7–12 years) in three distinct belt fit conditions: good, poor, and partially good fit. Parents were prompted to verbalise their thought processes while making the evaluation and were assessed on their knowledge regarding good seatbelt fit criteria.

Results Participants exposed to the 5-step test (n=18) showed a statistically significant improvement in their understanding of the criteria for achieving a good seatbelt fit. On average, they scored 1.0 point higher on the 6-point assessment compared to the control group (95% CI 0.23–1.7, p=0.012). Despite this greater knowledge, there was no significant difference between the two groups’ decisions about their child’s seatbelt fit (OR 2.08, 95% CI 0.52–8.34). Qualitative analysis of the ‘think aloud’ data indicates that parents possess some understanding of how to accurately determine a safe seatbelt fit for their child, yet also demonstrate supplementary metrics influence their decision beyond information provided in the 5-step test.

Conclusion The findings indicate that the 5-step test effectively enhances knowledge but offers inconclusive evidence regarding its ability to promote correct assessments about seatbelt fit. This implies that parents may need more support than is currently available, and merely grasping the essential criteria for safe seatbelt fit may not be sufficient for correct decision making. In future, user input should be incorporated into enhanced resources for parents guiding transition from booster seats.