From about age 12 years and up, students are progressively inducted into the mysteries of atoms, molecules and ions. In most classes, this induction involves students listening to teachers, reading books, and watching particle simulations. Students are expected to 'understand that scientific ideas about the particle nature of matter can be used to explain the properties of matter' and that 'ideas about the structure of the particles ... can be used to explain the different types of changes that can take place ...' (some typical outcomes in the Queensland School Curriculum Council science syllabus, 1999, pp.3031). Indeed, a vast array of biological, chemical and physical phenomena can only be explained by understanding the changes in the arrangement and motions of atoms and molecules. And so particles are frequently used in school and college textbooks to explain material properties, the states of matter and phase changes, chemical reactions, the water cycle, diffusion, DNA and cell biology.