This document discusses learner-centered psychological principles for child and adolescent development. It outlines 14 principles that are divided into cognitive/metacognitive, motivational/affective, developmental/social, and individual difference factors influencing learners and learning. The principles focus on internal psychological factors under the learner's control and acknowledge external contextual factors. They are intended to apply holistically to all learners to facilitate meaningful knowledge construction through strategic thinking and intrinsic motivation within social and developmental contexts.