Using two experiments, the authors examined the extent to which the scientific thinking circle can be used as heuristics to support scientific thinking in a classroom of children between the ages of 3 and 9 years old. To do this, the authors asked the children to build a bridge, raft, or electrical circuit using the material available to them. They checked the extent to which these children acted according to a number of physical laws. The results show that, compared with controls, 6-year-old children displayed significantly more operations in accordance with physical laws and significantly fewer operations which were counter to these physical laws after they have been instructed in the scientific thinking circle. The authors found no such effects in the other age groups. (Contains 8 figures.)