This article reports on answers by children (Grades 1–9) to oral and written questions concerning the phase change from liquid to gas. The development of concepts was followed, proceeding from concrete to abstract ideas. Difficulties in the application of abstractions were found, and participants were frequently misled where a choice of possible correct answers was given. Many students were found to experience difficulties in problem solving even though they may have had the necessary level of knowledge. These findings lead us to emphasize the importance of explaining specific situations and experiences using clear and relevant models to suit the discussion. To this end, a number of suggestions are made for minimizing misunderstandings and enhancing understanding.