This paper reports on the design of an on-line simulation that enhanced preservice teacher practicum experience in the important area of literacy teaching. Research with more than 200 users of the simulation showed that it developed pre-service teacher understanding of complex classroom situations associated with the teaching of literacy by giving them the opportunity to slow down or accelerate classroom events, revisit and reflect on critical decision points and replay events in the light of new understandings. This gave preservice teachers time to think critically about complex teaching situations which relied on the teacher's ability to tune into children's experiences, engage with them in dialogue and negotiation as well as utilise a range of indirect instructions such as questioning, modelling and prompting. Preservice teachers reported that their experience with the simulation enabled them to more fully appreciate the impact of subtle changes that experienced teachers made during lessons.