The document discusses depth and complexity as best practices for differentiated instruction in GATE programs. Depth involves examining topics from concrete to abstract levels, uncovering more details and new knowledge. It has dimensions like language of the discipline, details, patterns, trends, rules, ethics, and big ideas. Complexity includes making relationships between concepts and connecting ideas across disciplines. It encourages seeing associations among subjects from multiple perspectives. Complexity has dimensions of relationships over time, from different points of view, and interdisciplinary relationships. The document provides examples of how to teach these concepts using icons and higher-order thinking questions keyed to the different dimensions.