Background: The Researching Effective Approaches to Cleaning in Hospitals (REACH) study tested a multimodal cleaning intervention in Australian hospitals. This article reports findings from a pre/post questionnaire, embedded into the REACH study, that was administered prior to the implementation of the intervention and at the conclusion of the study. Methods: A cross-sectional questionnaire, nested within a stepped-wedge trial, was administered. The REACH intervention was a cleaning bundle comprising 5 interdependent components. The questionnaire explored the knowledge, reported practice, attitudes, roles, and perceived organizational support of environmental services staff members in the hospitals participating in the REACH study. Results: Environmental services staff members in 11 participating hospitals completed 616 pre- and 307 post-test questionnaires (n = 923). Increases in knowledge and practice were seen between the pre-and post-test questionnaires. Minimal changes were observed in attitudes regarding the role of cleaning and in perceived organizational support. Conclusion: To our knowledge, this is the first study to report changes in knowledge, attitudes, and perceived organizational support in environmental services staff members, in the context of a large multicenter clinical trial. In this underexplored group of hospital workers, findings suggest that environmental services staff members have a high level of knowledge related to cleaning practices and understand the importance of their role.