This study proposed a low-cost, easy to set up and easy to modify virtual classroom simulation environment, "CartoonClass," and tested its impact on 27 pre-service primary school teachers' noticing development during a semester-long mathematics methods course. The participants' perceptions of using CartoonClass were also examined. A Wilcoxon signed-rank test of the pre-test and post-test results showed that the participants (1) significantly developed their noticing skills, with regard to both general classroom events and attending-to skills; and (2) significantly changed their focus on 'mathematics thinking,' an accepted indicator of better noticing skills. (3) However, a novel video-summarising task aimed at detecting the participants' skills to quickly notice and grasp a complex teaching situation found no significant change in such ability over the course of the experiment. On the other hand, the qualitative data analysis showed the participants had positive perceptions of the virtual environment regarding realism, enjoyment and effectiveness.