Drawing on survey and administrative data on cooperating teachers (CTs) and their preservice student teachers (PSTs) in Chicago Public Schools during 2014-2015, this study offers an in-depth look at reports of how CTs engage in their mentoring roles during student teaching, and their influence on PSTs. Our sample includes CTs working with PSTs from across 44 teacher preparation institutions. Central to our analysis is an exploration of CTs as both models of effective instruction and as facilitative coaches on PST development. We find that both CT roles matter--PSTs feel better prepared to teach when their CTs model effective instruction and coach by providing more instructional support, frequent and adequate feedback, collaborative activity, job-search support, and a balance of autonomy and encouragement.