Conservation Tasks: What Are They And What Do They Show?

So what are conservation tasks? Such tasks test a child’s ability to recognise that certain properties are conserved, or are invariant, after an object, or set of objects, undergo physical transformations. These properties can include virtually anything – number, volume, length, or amount of matter in an object, for example.

The ability to recognise invariant properties is acquired, or perhaps a better way of putting it, is developed, in the transition between Jean Piaget’s Pre-operational stage, and his Concrete Operations stage. This transition is complete at around the age of seven, although no two children will develop this ability at exactly the same time since there are a multitude of biological and environmental factors that contribute to this development.

A classic test for the ability to conserve number is line up two rows of counters, each containing the same number, and arrange them so that each counter is paired up with another. When asked to compare the two rows, children of course say they are the same. Then one row is spread out so that the space between each counter increases, thus making one row longer than the other. When asked to compare the rows now, the children who have not fully developed the ability to conserve number claim that the longer row has more counters. This can happen even after the child has counted the rows and found them to be the same in number. It appears that the impact of the change in physical size of the row overrides the fact that the two rows were clearly the same in number when they were both of the same length.

The same basic misconception can occur when two identical vessels of liquid are filled to the same level and presented before a child who has not developed fully into Piaget’s Concrete Operations stage. Such children recognise that both vessels contain the same amount of liquid. They also see that when one of the vessels is emptied into a taller and thinner receptacle, the level of liquid is higher in the thinner vessel than in the other original vessel. Pre-Concrete Operations stage children conclude that there is more liquid in the thinner vessel, whereas those who have developed beyond that recognise that the volume of liquid must have remained constant.

The invariance of mass is also effected by size. This is seen when one of two identical balls of clay is re-formed into sausage shape. The child perceives the sausage shape as being bigger, thus concluding that it now has more clay.

There are other more abstract properties that children are unable to conserve before fully reaching the Concrete Operations stage. In a 1989 study by Kreil, children were told of a story where doctors took a horse and through a series of operations, made it look exactly like a zebra. They asked the child; “[when the doctors] were finished, was this animal a horse or a zebra?”. Around 65% of the children tested believed that the horse and actually been changed into a zebra. What this study also highlighted was that pre-operational children could sometimes conserve when the essential defining feature of an object was unchanged, even in the face of dramatic visual changes. This was shown when the aforementioned doctors altered a porcupine to look like a cactus. This time only 25% of the children tested believed that the porcupine had actually become the cactus. The rest recognised that one is an animal, the other a plant and one cannot become the other.

Piaget, having conducted many conservation experiments, concluded that children who are unable to conserve believe that a perceptual change means a quantitative change. Piaget believed that this confusion arose from pre-operational children’s lack of understanding of reversibility. Reversibility is the ability to see physical transformations and then imagine reversing them so that the change is cancelled out. Without being able to imagine, say, pouring the liquid back into the wider vessel mentioned above, the pre-operational child cannot see that the amount of liquid has remained constant throughout. This lack of reversibility causes a child to be dominated by the physical properties they perceive, hence they make incorrect conclusions about the perceived material. Piaget linked this lack of reversibility to pre-operational children’s inability to work out someone else’s viewpoint – i.e. the child believes that everyone perceives the world from the same perspective as their own.

Piaget used his reversibility ideas to formulate the Principle of Invariance. This principle states that there are relevant and irrelevant changes associated with quantity. For instance, addition and subtraction are relevant changes (since they change the quantity of an object or objects), while spreading out a row of counters, or re-forming malleable materials like clay, are irrelevant changes (since they change only physical properties, not quantity).

What is also evident from conservation tasks is that the development from pre-operational to operational is not sudden, but more gradual. For instance, children are able to conserve quantity in the counters problem around a year before they can conserve in the volume of liquid, or amount of matter problems.