Charles L. Wood, Crystalyn I. Goodnight, Keri S. Bethune, Angela I. Preston, & Samantha L. Cleaver (Learning Disabilities: A Contemporary Journal 14[2], 159-170, 2016):

Professional development through in-service training may not be of sufficient duration, intensity, and specificity to improve teachers’ instructional skills. Due to the increased need to support teachers’ use of evidence-based practices in multi-tiered systems of support such as RTI and PBIS, coaching can extend and strengthen professional development. This paper describes a multi-level approach to coaching, and provides implications for practice and research.