Some evidence supports the hypothesis that formal operational reasoning ability (at least that measured by Piagetian tasks) is a unified process. The purpose of this research was to determine: (1) if conservation tasks, such as conservation of number, liquid amount, weight and volume, are unifactor; and (2) if conservation tasks form a scale of…

An attempt to train concrete operational fifth-grade students (N=32) and seventh-grade students (N=32) to perform at the formal operational level on tasks demanding the control of variables are reported. The training was conducted in four individual sessions of approximately 30 minutes each. The training sessions were designed to represent a…