The purpose of this study was to investigate a proposed model for the acquisition of the concept of displacement volume and to compare two methods of conservation task presentation. A 12-stage hierarchical model for the acquisition of the concept was proposed, based on four primary assumptions: (1) concept attainment can be measured by conservation tasks; (2) there is a sequence of task attainments leading to displacement volume; (3) the child conserves displacement volume in continuous media before discontinuous media; and (4) the attainment of the concept of displacement volume depends equally upon the displacing object and the displaced medium. One hundred and twenty subjects, 40 from each of grades 3, 5, and 7, were selected from public schools in Tallahassee, Florida. Water was used as the continuous medium and blocks as the discontinuous medium to examine two configurations of conservation of displacement of volume. Results support the conclusion that the task used in this study was attained in the sequential order predicted by the proposed model. Analysis of variance revealed significant differences (at the .05 level) in task attainment between grade levels, but no significant differences were found between the two types of presentation (object or graphic). (GR)