The purpose of this study was to attempt to train the horizontality concept in a group of first graders who were non-operational on the horizontality concept but transitional on what Piaget has termed the precursor concepts of distance and length conservation. There were two groups of subjects (training and control), all of whom had failed a horizontality pretest. In the pretest they were presented with outline pictures of tilted jars and asked to draw in a water line as it would look if the jars were half full of water. One week after the pretest, children in the training group were seen in individual sessions and again asked to anticipate the water line by drawing a line on outline pictures of straight-sided jars. Subjects were given explicit knowledge of results as well as experience copying the actual water line. Results indicated a significant improvement for the training group which held to the follow-up posttest a week later. There was also transfer of training to a round-sided jar not used in training. Results are discussed in terms of Piaget's theoretical notions of assimilation and accommodation as related to explicit feedback and visual-motor practice. (Author/MS)