In this review, we evaluate developmental and personality research with the aim of determining whether the personality trait of conscientiousness can be identified in children and adolescents. After concluding that conscientiousness does emerge in childhood, we discuss the developmental origins of conscientiousness with a specific focus on self-regulation, academic motivation, and internalized compliance/internalization of standards. On the basis of the accumulated body of evidence, we conclude that self-regulation fosters conscientiousness later in life, both directly and via academic motivation and internalized compliance with norms. We argue that elements of conscientiousness are evident by early childhood; self-regulation skills are likely a core developmental component of conscientiousness; and despite the contribution of heredity to the aforementioned aspects of functioning, environmental factors likely contribute to conscientiousness.