वस्तु स्थायित्व (object permanence) की अवधारणा पियाजे के विकास के किस चरण के दौरान प्राप्त की जाती है?

According to Jean Piaget, mathematical knowledge is primarily acquired through:

How does Piaget's theory explain children's process of learning mathematical concepts?

A Class 2 teacher notices that when she pours water from a short, wide glass into a tall, thin one, her students insist that the taller glass holds more water. Based on Piaget's theory, which stage of cognitive development are these students most likely in, and what concept are they struggling with?