The purpose of this research study is to explore year 6, 8 & 11 (13, 15 and 17 years old respectively) Turkish pupils' views about the particulate nature of matter within the context of phase changes. About 300 pupils participated in the study. Questionnaires distributed to year 6, 8 and 11 pupils included 6-item open-ended questions about (a) arrangement and movement of particles in a solid, liquid and gas and (b) application of particulate ideas to explain phase changes. In addition to questionnaires, semi-structured interviews were carried out with pupils. Results indicated that many pupils, even older ones, had difficulties in applying the particulate theory to explain phase changes despite science teaching. The study has several implications for both teachers and curriculum designers.