Adolescents' capacity for moral reasoning expands due to :
Abstract thinking
During adolescence, according to Piaget's stage of formal operational thought, individuals develop the capacity for abstract thinking, allowing them to reason about hypothetical situations, ethical principles, and concepts like justice and fairness that are not tied to concrete, observable events.
This ability to think abstractly enables adolescents to consider multiple perspectives and underlying principles, which is essential for advanced moral reasoning, unlike the concrete, rule-bound moral judgments of younger children.
Physical height, sensory growth, and reflex maturity are physical or sensory-motor changes unrelated to the cognitive capacity required for moral reasoning.
Hence, adolescents' capacity for moral reasoning expands due to abstract thinking.