Final answer:
Piaget's concrete operational stage is where a child is most likely to master the skill of conservation.
Step-by-step explanation:
The skill of conservation is most likely to be mastered during Piaget's concrete operational stage. This stage occurs from about 7 to 11 years old. In the concrete operational stage, children can think logically about real (concrete) events and understand the concept of conservation.
Jean Piaget, a Swiss psychologist, proposed a theory of cognitive development that outlines distinct stages through which children pass as they develop intellectually. Piaget's theory emphasizes the qualitative changes in thinking that occur at each stage.