Nurturing reflective teaching and improving critical-thinking instruction are two important goals in teacher education, but these are only achievable when teachers-in-training are provided with opportunities for building professional knowledge and for exhibiting reflective teaching practices. A computer simulation program (CS-TGCTS) was therefore developed here, and its effectiveness is explained in this study. From 149 preservice teachers participating in this study, a pretest-posttest control group design was defined by four student groups and two treatments. The central hypothesis was that increasing participants' self-awareness of teacher behaviors and enhancing mindful learning in professional knowledge would provoke reflective teaching and further bring about improvements in teacher behaviors. The findings support the hypothesis and suggest that the CS-TGCTS simulation is an effective vehicle for improving preservice teachers' reflective teaching in critical-thinking instruction.