This chapter explains the biological embedding of trauma in the nervous system and brain. It describes how survival responses—fight, flight, freeze, and fawn—manifest in the classroom and interfere with higher-order thinking. Chronic activation of stress systems leads to allostatic load, resulting in long-term health challenges. Developmental timing is highlighted, showing that early trauma has profound impacts on brain architecture. For educators, this science underscores the need to create predictable, regulated, and safe environments where students can shift from survival to learning.