Samuel and Bryant (5)
Strengths: S&B's experiment had a high level of control over possible confounding variables. The children had four attempts at each conservation task which eliminates the possibility that the children answered incorrectly or correctly by chance, and order effects were controlled for by varying the order of presentation of the tasks,
Weaknesses: S&B also criticise Piaget for emphasising how children as individuls. S&B argue that children don't learn in isolation and that they learn far more readily and efficiently when they work together then when they are alone. On the number task the children could have counted the number of counters used and this could account for level of accuracy on the number task. On the other two tasks (volume and mass), the children couldn't tell by looking at the materials how "much" they consisted of. A further weakness could have been that the children might have felt nervous doing the tasks (perhaps the younger children more so) and therefore resulted in the answers being spontaneous rather than thought out. The sample isn't representative of all children in the UK as the study was conducted in Devon.
Implications: Do longitudinal study of children’s ability to conserve. Study same children over a number of years and use a larger sample and from more than one area (the original was Devon) This would make it more valid and representative. Use juice or sweets for the tasks as it is more ecologically valid.
Effect to the results: Get more children being able to conserve younger. Still expect conservation to improve with age and number better than mass then volume. Maybe less errors with the one judgment task.