An overview of the most influential research on student motivation, engagement, and 21st-century skills. This paper, originally published in 2012 and revised by in 2014 by Youth Development Executives of King County, presents a holistic framework for thinking about student success. It provides operational definitions for the skills and dispositions that matter most, and suggests ways that educators, parents, and out-of-school-time program providers can begin to measure these skills in young people. This is the first of a two-part series. The second part covers strategies for building motivation, engagement, and 21st-century skills.