This brief is one in a series aimed at providing K-12 education decision-makers and advocates with an evidence base to ground discussions about how to best serve students during and following the novel coronavirus pandemic. Rigorous research provides strong evidence that high-dosage tutoring can produce large learning gains for a wide range of students, including those who have fallen behind academically. This brief provides information on design principles for effective tutoring including: frequency, group size, personnel, focus, measurement, relationships, curriculum, scheduling, delivery mode, and prioritization. [This brief was prepared in collaboration with the University of Virginia, School of Education and Human Development.]