Samuel and Bryant (1983)
252 boys and girls from a variety of Devon schools and pre-schools. Placed into 4 age-controlled groups (A,B,C,D).
Three conversation tasks using different materials were then carried out; counters for numbers; Plasticine for mass; Liquid in a glass for volume.
Standard- Using Pre and Post transformation questions.
One-Judgement- The question is only asked after transformation.
The ability to carry out a conservation task correctly increases with age.