The purpose of this article is to share results of a mixed-methods research study designed to shed light on similarities and differences between school-employed and agency-employed school-based social workers' preparation and practice as a precursor for collaboration in expanded school mental health. Online survey data from a national sample of 186 school-based social workers and focus group data from a convenience sample of 10 school-based social workers in a large urban area were analyzed, revealing more similarities than differences between the school- and agency-employed social workers. Data revealed that there were no significant differences in educational preparation between the two groups and that knowledge about each others' roles is most likely learned on the job. Postgraduate in-service training, including problem-based learning, is suggested as a vehicle to expand knowledge and skills so as to decrease duplication of services and maximize complementary roles and collaboration between these two types of school-based social workers.