We describe the research and development of an NSF-funded, five-year experimental program to strengthen informal (out-of-school) STEM learning by youth in five rural communities. The central component of the model was a cadre of community members known as 'STEM Guides' who were hired to work as brokers between youth and the STEM learning resources potentially available to them. These STEM Guides were respected adults with credible connections to youth, flexible schedules, the ability to travel within the community, and enthusiasm for identifying local STEM resources. The Guides were trained and supported by the project staff of an educational research and development non-profit, whose researchers studied the Guides' experiences over several years as they reflected on the ways they could support youth to pursue STEM outside of school. This project was unusual in developing embedded rural residents to take a professional brokering role with youth aged 10-18 throughout a region of several neighbouring towns, instead of relying on parents or teachers to provide such connections opportunistically and only for their own youth. Taking an ecosystems perspective, this article highlights some of the opportunities and challenges these STEM brokers faced as they tried to catalyze connections for youth in their communities.