Science, Technology, Engineering, and Math (STEM) education is essential to the economic growth, health, and progress of the modern world. One cognitive ability that underpins thinking and learning in STEM, as well as other disciplines, is relational ability. This ability to spot common relations shared by different objects, events, ideas, or representations and generalize them beyond the current context is the cornerstone of human cognition (Gentner, 2003, 2010; Goldwater & Schalk, 2016). Our ability to compare across multiple representations and highlight relational commonalities is the process that facilitates relational learning and subsequently, relational abstraction (Gentner, 1983; Gentner & Hoyos, 2017). As relational ability has been argued to be a key component of higher-order cognition (Richland & Simms, 2015), it is important to investigate its developmental trajectory and the factors that facilitate and hinder this ability. Understanding these factors will enable us to create environments that foster learning and discovery for all ages. Humans are born with a powerful structure-mapping mechanism that enables us to learn abstract relations. Our relational ability improves dramatically over time, but despite these changes, there are common signatures of relational abilities that are consistent across development. In addition, perceptual, linguistic, cognitive, and methodological factors also influence relational learning and performance. This dissertation examines the origins of our relational abilities and its trajectory of development with a specific focus on infancy and early childhood. Chapter 1 provides a brief introduction about the various factors that facilitate and hinder relational ability. Chapter 2 examines the variation in encoding processes and how that influences relational learning in infants. Chapter 3 investigates how methodological factors influence spontaneous relational performance among preschoolers. Chapter 4 investigates whether one perceptual factor -- relational redundancy -- facilitates or hinders relational performance and generalization. Taken together, these studies highlight that our relational learning mechanism is present early in life, it highlights aspects that are continuous throughout development, and examines various factors that can impact learning and cognition during the first years of life. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]