From the article: "Tutoring ranks among the most versatile and potentially transformative educational tools available. Dozens of randomized experiments have evaluated preK–12 tutoring programs, varying widely in approaches, contexts, and costs. This article presents results from a systematic review and meta-analysis of tutoring field experiments. We develop a framework for understanding variation in tutoring program impact and examine effect sizes (ESs) across a range of characteristics. We find that tutoring programs yield consistently substantial positive impacts on learning, with an overall pooled ES of 0.288 SD (SE = 0.029, p < .001). ESs tend to be largest for programs that use teachers or paraprofessionals as tutors, are held in earlier grades, occur at least 3 days per week, and are held during school."