We had a study on the various thinking of weight in children and found out that some children did not construct the concept of the conservation of weight by the height. We had possible training for construct these concept and had study these effectiveness. After this studies we identified that the concept of the conservation of weight by the height developed between the ages of 5-9 years and at 9 years, about 80% of them had acqired an understanding of concept. In 5 years old children we found out that they were able to develop this concept of weight when trained in this direction. It seem effective to deep the interest and concern when they use the platform scales in their training.