This paper reports the findings of a study exploring the use of a software package to help pupils understand particulate explanations for melting and evaporation below boiling point. Two matched classes in a primary school in Greece (ages 11-12, n = 16 and 19) were involved in a short intervention of six one hour lessons. Covering the same phenomena and particle ideas, one class was taught using the software simulations, the other was not. Data were collected pre and post intervention through individual interviews (n= 2 x 12). In an approach which included the ideas of an 'ability to hold' and a distribution of energy, both groups made progress, but there were indications that the software had helped and more so for evaporation. However, in other cases, pupils could not escape from their initial views and created synthetic explanations with both macroscopic and microscopic characteristics. (Contains 3 tables 10 figures.)