This document reports on a study of 48 kindergarten children in Israel regarding their concepts of "solid" and "liquid." Children were asked to classify a set of 30 materials into two groups (a group of 9 liquids and a group of 21 solids). About 65% could classify liquids correctly, 50% could classify rigid materials correctly, 30% related non-rigid materials to the group of solids, and only about 20% classified powders in the group of solids. The majority did not use a consistant and systematic set of criteria to classify all the materials. In addition, they tended to change their criteria during the course of classification. They used such criteria as color, weight, function, usage, and spatial relatedness. (TW)