Although published in 2006, The Tutoring Revolution: Applying Research for Best Practices, Policy Implications, and Student Achievement by Rowman & Littlefield Education comprehensively discusses the importance of the benefits of tutoring for students based on research-driven results.  Their recommendations provide an excellent resource for tutors nationwide and one of their conclusions is that tutoring, in-home tutoring programs in particular by well-trained professionals, can have a significant impact on learning outcomes.