Two purposes guided this mixed-methods investigation of the collaborative mentoring of teachers in a large school system in the south-eastern United States. The first was to examine collaborative mentoring as unstructured peer-to-peer coaching that emerged spontaneously as teachers shared experiences about effectively teaching English language learners (ELLs). The second was to examine how licensure courses contributed to the emergence of collaborative mentoring. Data collection consisted of questionnaires, mentoring stories, phone interviews, and electronic surveys. After completing courses, 84 teachers reported significant increases in frequency and duration of interactions for sharing best practices with colleagues. The data analysts identified course components, causal links, and catalysts as having created conditions for mentoring. Of 33 novice teachers recently trained in teaching ELLs, most found themselves mentoring veteran teachers yet untrained in teaching this student group. This unexpected reversal of the traditional novice/veteran roles within mentoring dyads addresses a gap in the educational literature. (Contains 3 tables.)