Prior research has connected characteristics of cooperating teachers who supervise student teaching to performance measures of the teacher candidates they host, suggesting more effective teachers may also be better mentors. The specific measures of cooperating teacher effectiveness considered in this prior literature (value added and performance evaluations), however, are infrequently observable to individuals responsible for student teaching placements. In this paper, we consider a more easily observed proxy for mentor effectiveness: National Board (NB) Certification. We find that NB teachers are considerably more likely to host candidates than other teachers, candidates supervised by NB teachers are slightly more likely to be hired within three years, and these candidates have slightly lower value added in English language arts than their peers, all else being equal. We find no significant relationship between cooperating teacher NB certification and candidates' later attrition and value added in math. We conclude that individuals and policies seeking to leverage student teaching placements to improve student and teacher outcomes may need to focus on less easily observable proxies of cooperating teacher quality than NB certification status.