This chapter describes the first phase of the Friends of the Children randomized controlled trial (RCT), The Child Study (N = 278). The study occurred in partnership with four independent Friends of the Children nonprofit organizations, called “chapters,” that deliver the program in the neighborhoods within which they are located. Chapters worked with their local public school districts and partner elementary schools to identify eligible children in kindergarten or first grade for their professional youth mentoring program. Children were randomly assigned to an intervention condition, in which they were invited to be matched with a mentor and to be a part of program for 12 plus years, or to a referral only control condition. Prior to the launch of the study, informed consent was sought from caregivers to participate, and assent was sought from children. For enrolled participants, assessments were conducted before the intervention began and then in each of the subsequent five years, until the end of fifth or sixth grade. Within the intervention condition, 92% of children met with their assigned mentor. During the five years of the study, 54% of children in the intervention condition had the same mentor throughout, and the remainder has multiple mentors. By the end of the five years, 81% still had a mentor and another 6% were waiting for a new mentor. Across the period of the study, several statistically significant differences were found between the two conditions, with each effect being more favorable for children in the intervention condition. The RCT continues today as the Young Adult Study.