Effective classroom teachers have always personalized learning. But they have done so with limited structural supports, such as curriculum, pedagogy, tools, and resources specifically designed to support personalization. For the education community to bring personalized learning more systematically to many more learners, research about how students learn needs to be leveraged so the accuracy and precision of personalization can be improved. This paper focuses on four points: (1) Personalized learning must begin with research; (2) Technology can be used to translate research to support learner variability for personalized learning practices providing structures, strategies, and scale; (3) In the push for a common understand of "what" personalized learning is, it is critical not to lose sight of the "why"; and (4) Understanding learners creates pathways to success.