The place of simulation in teaching mathematical modelling has been advocated previously by a number of authors. It is argued here that the skill of integrating simulation and analytical investigation of physical systems in a mutually supportive way is necessary and valuable for the practising applied mathematician. A module, included in a course on systems theory, designed to help students to develop this skill is described. The necessity of having an accessible system simulation package, which is easy to learn and use, available to the students is emphasized.