<P> One example of an experiment for testing conservation is the water level task . An experimenter will have two glasses that are the same size, fill them to the same level with liquid, which the child will acknowledge is the same . Then, the experimenter will pour the liquid from one of the small glasses into a tall, thin glass . The experimenter will then ask the child if the taller glass has more liquid, less liquid, or the same amount of liquid . The child will then give his answer . The experimenter will ask the child why he gave his answer, or why he thinks that is . </P> <Ul> <Li> Justification: After the child has answered the question being posed, the experimenter must ask why the child gave that answer . This is important because the answers they give can help the experimenter to assess the child's developmental age . </Li> <Li> Number of times asking: Some argue that if a child is asked if the amount of liquid in the first set of glasses is equal then, after pouring the water into the taller glass, the experimenter asks again about the amount of liquid, the children will start to doubt their original answer . They may start to think that the original levels were not equal, which will influence their second answer . </Li> <Li> Word choice: The phrasing that the experimenter uses may affect how the child answers . If, in the liquid and glass example, the experimenter asks, "Which of these glasses has more liquid?", the child may think that his thoughts of them being the same is wrong because the adult is saying that one must have more . Alternatively, if the experimenter asks, "Are these equal?", then the child is more likely to say that they are, because the experimenter is implying that they are . </Li> </Ul> <Li> Justification: After the child has answered the question being posed, the experimenter must ask why the child gave that answer . This is important because the answers they give can help the experimenter to assess the child's developmental age . </Li> <Li> Number of times asking: Some argue that if a child is asked if the amount of liquid in the first set of glasses is equal then, after pouring the water into the taller glass, the experimenter asks again about the amount of liquid, the children will start to doubt their original answer . They may start to think that the original levels were not equal, which will influence their second answer . </Li>

According to piaget the concrete operational stage is the highest level of cognitive development