In this pilot study, we sought to examine the influence of the beliefs of Grade 10 to 12 physical science teachers on their intended and actual usage of interactive simulations (Physics Education Technology, or PhET) in their classrooms. A combination of the Theory of Planned Behaviour, the Technology Acceptance Model and the Innovation Diffusion Theory was used to examine the influence of teachers' attitudes, subjective norms and perceived behavioural control on their intention to use simulations in their classrooms. Using regression and factor analyses, it was found that beliefs about the perceived usefulness and the pedagogical compatibility of PhET have a significant effect on teachers' attitude towards the use of the simulations in their classrooms. The expectations of the teachers' colleagues contribute to the subjective norm of these teachers. The regression and partial correlation result also highlights the importance of teachers' general technology proficiency. Although we were not able to confirm a direct link between attitudes, subjective norm, perceived behavioural control, and the teachers' behaviour intention we show the influence of behaviour intention on the actual use of the simulations with an accuracy of 70.83%.