There is considerable variation in how providers of digital education describe what they do, their services, how students access services, and what is delivered, complicating efforts to accurately assess its impact. We examine program characteristics of digital tutoring providers using rich, longitudinal observational and interview data and then analyze student attendance patterns and effects of digital tutoring on low-income students' reading and mathematics achievement. We find significant associations between formats, curriculum drivers, tutor locations, and other characteristics of digital providers and their effectiveness in increasing student achievement, as well as differential access by student characteristics, that warrant further investigation as digital providers' roles in K-12 instruction continue to expand.