Coaching models are increasingly used in schools to enhance fidelity and effectiveness of evidence-based interventions; yet, little is known about the relationship between the coach and teacher (i.e., coach–teacher alliance), which may indirectly enhance teacher and student outcomes through improved implementation quality. There is also limited research on measures of coach–teacher alliance, further hindering the field from understanding the active components for successful coaching. The current study examined the factor structure and psychometric characteristics of a measure of coach–teacher alliance as reported by both teachers and coaches and explored the extent to which teachers and coaches reliably rate their alliance. Data come from a sample of 147 teachers who received implementation support from one of four coaches; both the teacher and the coach completed an alliance questionnaire. Separate confirmatory factor analyses for each informant revealed four factors (relationship, process, investment, and perceived benefits) as well as an additional coach-rated factor (perceived teacher barriers). A series of analyses, including cross-rater correlations, intraclass correlation coefficients, and Kuder-Richardson reliability estimates suggested that teachers and coaches provide reliable, though not redundant, information about the alliance. Implications for future research and the utilization of the parallel coach–teacher alliance measures to increase the effectiveness of coaching are discussed.