Background: Prescribing is a complex task with potential for many types of error to occur. Despite the introduction of a standard national medication chart for Australian hospital inpatients in 2006, simple prescribing errors are common. Aim: To compare the effect of quality improvement initiatives on the rate of simple prescribing errors. Design: A prospective, multisite comparison of prescribing education interventions. Methods: Using three hospital sites, we compared site-specific changes in prescribing error rates following use of an online education module alone (low intensity) with prescribing error rates following a high-intensity intervention (comprising the same online education module plus nurse education and academic detailing of junior prescribers). The study period was 4 months between May and August 2011. Results: Full completion of the adverse drug reactions field did not improve after either intervention; however, there was better documentation of some elements following high-intensity intervention. Prescriber performance improved significantly for more elements in the regular prescription category than any other category of prescription. Legibility of medication name improved across all categories following interventions. Clarity of frequency, prescriber name and documentation of indication improved following both high- and low-intensity intervention. Conclusions: Improvements were seen in several prescription elements after the intervention but the majority of elements that improved were affected by both low- and high-intensity interventions. Despite targeted intervention, significant rates of prescribing breaches persisted. The prevalence of prescription breaches partially responds to an online education module. The nature of any additional intervention that would be effective is unclear.