While educational technologies such as MOOCs have helped scale content-based learning, scaling situated learning is still challenging. The time it takes to define a real-world project and to mentor learners is often prohibitive, especially given the limited contributions that novices are able to make. This paper introduces micro-role hierarchies, a form of coordination that integrates workflows and hierarchies to help short-term novices predictably contribute to complex projects. Individuals contribute through micro-roles, small experiential assignments taking roughly 2 hours. These micro-roles support execution of the desired work process, but also sequence into learning pathways, resulting in a learning dynamic similar to moving up an organizational hierarchy. We demonstrate micro-role hierarchies through Causeway, a platform for learning web development while building websites for nonprofits. We carry out a proof-of-concept study in which learners built static websites for refugee resettlement agencies in 2 hour long roles.