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 synthesis of ideas concerning the mechanisms of development put forth by Piaget, Ausubel, Bruner, and C. Lawson. The training was successful (p < .001) and specific transfer of the trained concept was obtained for both samples. Pretest level of intellectual development was significantly related to success on posttest tasks of specific transfer (p < .10). On one posttest task designed to measure nonspecific transfer, the trained seventh-grade subjects scored significantly higher (p < .05) than the control subjects. The effectiveness of the training suggests that properly designed instruction, which is based on students' intuitive conceptual understanding at the concrete level, can raise this intuitive understanding to the level of a meaningful verbal rule which then can be successfully applied in a variety of problem situations. (Author)